Regulation of Cancer Cell Proliferation Using siRNA Technology - Research Paper Example

siRNA and cancer Introduction Researchers have been tying for decades to explain the molecular mechanisms at the play of the cells that cause cancer development. There is now developing evidence that cancers may emerge from cancer stem cells. In some way, a group of cells develops that are immortal and are able of producing progenitor cells which can grow; however, research communities does not know how these cells mislay, loosing control (Acton 13). Recent studies have proposed the existence of an extraordinary small sub-population of cancer cells which act as tumor-instigating cells or the cancer stem cells. Background The cancer stem cells are connected to maintain the unlimited and self-renewal growth capabilities of cancer while only consist of a small potion of the tumor. Consequently, cancer stem cells might be responsible for tumor progression, metastasis, and drug/treatment resistance development. Other studies have proved that small interfering RNAs (siRNAs) play a big on what genes are expressed or not expressed through gene silencing capabilities (Acton 47). Excitingly, siRNAs might provide some new perception into the complexities of cancer. These siRNA molecules could hold a huge potential therapeutically in the fight against cancer. This paper, discuses the functions of siRNAs and cancer stem cells and explain the link between these 2 topics. The paper also present methods to employ in current and forthcoming research to study the topics and expound upon different molecular therapy options that may have implications in altering cancer stem cells dysregulation and fighting oncogenesis. Discussion siRNAs relation to cancer stem cell RNA interference is a key system within cells that assist control which genes get actived and to what degree they get activated. The 2 central RNA interferences are the small interfering RNA (siRNA) and micro RNA (miRNA). Both play a role in gene silencing. The siRNAs originate from procession of long, double-stranded RNA and target the miRNAs for degradation using full complementary sequences. Meanwhile, miRNAs are derived from procession of short RNAs hairpins and silence expression of gene through translational repression or miRNA degradation with partially complementary target orders. However, there is a more important difference. The siRNAs are regularly of exogenous origin, while the siRNAs are endogenously encoded. For this fat, the use of siRNAs has attracted many researchers because of their reliability and efficient application to developing therapeutics in combating diseases like cancer. Procedure and working analysis The biogenesis of siRNAs has been studied and reviewed by many investigators. To start with, RNAs are recorded by the polymerase II enzyme generating a long primary-siRNA (pri-siRNA) in the nucleus. Post-transcriptional modifications involve a 5’ final cap structure and a 3’ final poly-adenylated tail which flank the pri-siRNAs (Acton 281). This suggests that pri-siRNAs are functionally and structurally similar to RNAs. Addition to the 5’ cap and the 3’ tail, pri-siRNAs contain specific hairpin-formed stem-loop constructions of ~70 nucleotides. The stem-loop structures are acknowledged and cleaved by approximately ~650 kDa nuclear micro-processor compound consisting of RNase III endonuclease Drosha plus the essential DiGeorge syndrome crucial region gene eight (DGCR8) binding protein, which produces a ~70 nucleotide hairpin intermediate (Acton 440). The resultant ~70 nucleotide hairpin intermediate (the pre-siRNA) is transported from the nucleus into the cytoplasm courtesy of Exportin-5 and its co-factor Ran-GTP (Acton 441). While in the cytoplasm, pre-siRNAs are further cleaved. The resulting cleavage is carried out of the cytoplasm by RNase III endonulease Dicer1 and its essential transactivation response of RNA binding protein (TRBP). This produces a short deficient double stranded siRNA duplex. Helicase then undoes this imperfect siRNA duplex into a mature siRNA. Then, TRBP recruits the catalytic Argonaute2 to the Dicer complex while the mature siRNA forming a RNA-induced silencing complex (the RISC) (Acton 75). The RISC subsequently controls gene expression by RNA degradation or translational repression by partially complementary sequences in 3’-untranslated region (or 3’-UTR) of the targeted RNA. In animals, siRNAs may also do the same by targeting the coding areas of RNAs. Therefore, siRNAs negatively control gene and protein expression by the RNA (RNAi) interference pathway. Recently, siRNAs have been associated to have a stake in stem cell functioning. Stem cells are found allover the human body and they are essential to tissue repair, replacement, and development. This is because the height of expression of certain siRNAs is different on stem cells compared to other normal tissues. Studies have analyzed siRNA expression profiles in homogeneous human embryonic stem cells, partly differentiated embryoid tissues, and terminally differentiated cells. One analysis discovered that 104 siRNAs and 778 genes were differentially expressed within the 3 cells types. Another study discovered rapid regulation of certain siRNAs in response to differentiation. In addition to siRNA expression profiles, researchers have used Dicer1 (dcr1) mutants to confirm siRNAs’ regulation of stem cells (Acton 426). Discussion As discoursed above, Dicer1 plays a significant role in siRNA biogenesis; thus, a mutant dcr1 would offer great understanding into a proposed function of siRNAs in stem cells. A loss of dcr1 resulted in premature death in mouse replicas and depletion of the stem cells in mouse. This suggests that siRNAs do play a substantial part in stem cell regulation since a disruption of the siRNA pathway results to a decreased stem cell populace. Another study found that mutated dcr1 in an embryonic mouse stem cells causes reduced siRNA expression and severe weaknesses in stem cell differentiation on vivo and vitro; additionally, re-expression of Dicer1 reversed these phenotypes. These dcr1 mutants’ data demonstrate that siRNAs have a fundamental part in regulating the stem cell function (Acton 38). siRNAs can also function in stem cell science through an epigenetic regulation. Epigenetic regulation, with modification of histone and also DNA methylation is known to take vital part in regulating stem cell differentiation and proliferation. A DNA methyl-CP-binding protein (MeCP2) has been revealed to epigenetically regulate particular siRNAs in adult neural stem cell. This is a rather stimulating finding because the relationship (if any) between the siRNA and epigenetic pathways remains not well understood. This result demonstrates that there is special cross talk between the siRNA pathway and epigenetic regulation. This cross talk can be important to modulate stem cell function and differentiation. Changes in histone modifications and DNA methylation are also characteristic of cancers. These epigenetic changes result to dysregulation of genes expression profiles bringing about development and progress of cancer disease states. siRNAs could be affected in one way or another by these epigenetic changes as a result of the cross talks between the 2 pathways. There are extensive changes in siRNA expression profiles during tumorigenesis. Therefore, siRNAs’ role in stem cells regulation and cancer development and progression are an outstanding area of research. Cancer stem cells self-renewal Stem cells are demarcated by their multi-lineage variation and their ability to go through self-renewal. This self-renewal ability can be either symmetric or asymmetric. Self-renewal is unique from other cell proliferative processes since at least one of progeny is alike the original stem cell. In all the other replicative courses, the progeny of division undertake a series of differentiation procedures (Acton 168). In asymmetric cells self-renewal, one of these two progeny is accurately identical to the original stem cell, while the other cell remains a committed progenitor cell that undergoes cellular differentiation. Since one stem cell comes from a product of an asymmetrical self-renewal division, stem cell number is preserved. However, symmetrical self-renewal, 2 stem cells are produced, causing stem cell expansion. Both differentiation and self-renewal of stem cells are controlled by the stem cell niche that is the micro-environment surrounding the stem cell. Lately, evidence has developed that suggests that a minor subset of cancer cells on tumors have stem cell characteristics. The cancer stems cell assumption contends that cancers are got from a small portion of cancer cells that create a reservoir of independent cells with the exclusive capability of self-renewing and initiating /maintaining tumor. According to this cancer theory on stem cell, the cancer stem cells remain to be tumor initiating cells which proliferate exclusively through self-renewal. The cancer stem cells are believed to only comprise of a small part of the tumor, but can be responsible for tumor extension, progression, metastasis, and treatment/drug-resistance (Acton 19). Thus, it has been put forward that to be maximally effectual, cancer therapy should be focused against the cancer stem cells. The question then begs – How does uneven self-renewal capabilities happen in cancer stem cells? Evidence is growing that several pathways that have routinely been connected to cancer regulate the normal stem cell development too. This evidence submits that these signaling pathways hold a significant part in dysregulating stem cell genes in cancerous stem cells causing the formation and development of tumors. The Bcl-2, Wnt, Hedgehog, CD44, Bmi-1, HMGA2, and Notch pathways have been found to be playing a part in the self-renewal, survival, and differentiation of cancerous stem cells (Acton 361). Cancer stem cells and siRNA connection in supporting oncogenesis are abnormal expression levels of siRNAs in cancer. Tumors evaluated by siRNA profiling have been determined to have significantly different siRNA profiles compared to other normal cells from same tissue. In addition, siRNAs have been found with a convincing evidence to be significant factors in stem cell science. Using cDNA cloning, multiple siRNAs have been identified to be exceptionally expressed in the human embryonic stem cells as compared to their differentiated complements. Based on these discoveries, it is rather interesting that undifferentiated stem cells show expression profiles of siRNAs that are indicative of cancer cells. Still, more research has allowed people to merge this obvious equivalent even further. Recent evidence demonstrates that there is a distinctive sub-population of cancer cells performing as cancer stem cells in tumors that have the aptitude to self-renew - hence initiating, maintaining, and progressing cancer. Aberrant genes expression and function are mark characteristics of cancer. Consequently, it is supposed that genetic alterations from assimilated epigenetic abnormalities initiate dysregulation of genes in cancer stem cells (Acton 69). The cancer stem cells can escape the limits of the stem cell position because of the dysregulation. This results to self-renewal potential. Micro-environmental signals or factors are thought to account for cancer stem cells’ epigenetic aberrations, resulting in the silencing or interference of certain genes (Acton 370). Therefore, an underlying sub-cellular progression must account for cancer stem cell dysregulation. There are two common abnormalities in all cancer cells— they display dysregulation of cell cycle resulting in uninhibited growth and they are resilient to death due to abnormalities in one or several proteins that intercedes apoptosis. The aim for RNAi approaches in cancer therapy are hence to knock out the cell cycle gene expression and an anti-apoptotic gene on the cancer cells thus stopping tumor development and killing the cancerous cells. To selectively eradicate cancerous cells without damaging the normal cells, RNAi will be targeted to genes specifically involved in the survival or growth of the cancer cells, or the siRNAs will be selectively delivered to the cancerous cells. For many years antisense oligo-deoxy-nucleotide technology was pursued in pre-clinical studies of cancer, however, with discouraging results generally. Recent studies have clearly confirmed advantages of RNAi methods of growth suppression and terminating of cancer cells (Acton 246). Studies have proven that siRNA is greater than orders of magnitude more strong than antisense DNA in the suppression of gene expression in human cancer cell lines. Activation of the tumor necrosis factor (TNF) corresponding receptors and linked death receptors can prompt death of some cancerous cells, but may concurrently activate pathways that encourage cell survival; one protein which inhibits the TNF cells death pathway is called FLICE-like inhibitory protein (FLIP). When FLIP expression is suppressed in cancer cells by use of siRNAs, the cells become more sensitive on being killed when the death receptors were activated. Conclusion As we have seen in the above paragraphs, abnormal siRNA expression profiles of oncogenic or tumor suppressor siRNAs are associated to the activation of stem cells signaling pathways in the cancer stem cells. Such dysregulation of cancer stem cell leads to disease initiation, development, metastasis, progression, resistance to existing treatments, and relapse among patients. Accordingly, the development and usage of molecular siRNA therapies are imperative in addressing oncogenesis. Additionally, and maybe more essentially, effective and efficient targeting, packaging, and delivery of these siRNA-based therapeutics requires to be addressed. Nano-particle technology could hold the basic to accomplishing this. Consequently, future research should aim at developing nanoparticle delivery methods as well as revealing the subcellular intricacies of siRNA regulating cancer stem cell’s self-renewal potential and abilities. Defeating cancer stem cells dysregulation through molecular siRNA therapies could help in the battle against cancer progression, relapse and resistance. The distinct and clear association between abnormal expression levels of certain siRNAs and dysregulation cancer stem cells bids the scientific community a unique opportunity to combat cancer initiation and continuous development through the employment of molecular siRNA therapies that aim oncogenic or tumor suppressor siRNAs. In theory, molecular siRNA based cancer therapy should eradicate the cancer stem cells ability of self-renewal, significantly reduce the resistance of cancer to contemporary cancer treatment, and hamper relapse in sick patients. Works Cited Acton, Q. Ashton. Cancer: New Insights for the Healthcare Professional: 2011 Edition. New York: ScholarlyEditions, 2011. Read More