Regulation Mechanism Of RPS15A In Promoting Leukemia U937 Cell Proliferation

Leukemia is a common hematological malignant tumor. In recent years, the incidence and mortality of leukemia have been increasing with a low rate of surgical resection, high invasive ability and poor prognosis. According to some statistics, the highest incidence of leukemia happened in Europe and America which was around 3.2-7.4 cases in 100 thousand people. As the gradual deterioration of ecological environment, the incidence of leukemia is increasing every year in China. Although there is a large amount of data demonstrating that most of leukemia cases were caused by gene mutation, the potential molecular mechanism of leukemia is still limited. Clarifying the role in the pathogenesis of leukemia, looking for effective drug targets for leukemia treatment and developing specific drugs for leukemia are major tasks and challenges for biomedical and clinical researchers.In recent years, leukemia patients are usually treated with radiotherapy, chemotherapy or hematopoietic stem cell transplantation. However, the patients always respond to radiotherapy and chemotherapy strongly and feel difficult to afford the high cost of hematopoietic stem cell transplantation. With the progress of oncology and molecular biology, the mechanism of cancer receives increasingly attention and becomes the research hotspots of global biomedical researchers. A large number of studies have shown that several molecules participate in the initiation and development of leukemia cells and most of the molecules play an important role in cell proliferation, differentiation and apoptosis. At present, studies have shown that abnormalities occur in ribosome biogenesis and protein translation would affect the process of cell growth and cell cycle, resulted in tumor. Many studies reported that the abnormal expression, mutation or imbalance of ribosomal protein in organisms could be a reason of the initiation of cancer.Ribosomal protein is an essential part of ribosome which plays an important role during the progress of translation. There are researches have demonstrated that many ribosome proteins are regulated by their post-transcription level during their synthetic processes. And some biodegradation pathways of proteasome in cells such as phosphorylation and ubiquitination are also involved in the post-transcriptional regulation of ribosome protein. Ribosome could also mediate protein biosynthesis, regulation of cell proliferation, differentiation, apoptosis, and DNA repair. Recent studies have confirmed that ribosomal proteins are involved in the regulation of biological cell carcinogenesis processes. Ribosome proteins are usually high expressed in malignant tumor cells and enhance the cell proliferation, invasion and migration abilities of the tumor cells.Ribosomal protein, as a carcinogenic gene, is involved in many kinds of cancers process, including esophageal cancer, gastric cancer, lung cancer. It is a hot spot in the research of targeted cancer therapy. RPS15A gene is a member of ribosomal protein gene family. The RPS15A gene is located on the chromosome 16p13, which has the coding region of 393bp containing five exons. The expression of RPS15A gene was regulated by multiple genes. The structure of RPS15A gene is highly homologous to the prokaryotic RPS8 gene. A new meta-analysis showed that RPS15A expression was increased in astrocytoma, colorectal cancer and prostate cancer. In addition, more and more studies have confirmed that the RPS15A gene is involved in the growth of some tumors, such as liver cancer, osteosarcoma and lung cancer. But its functional role in leukemia remains unknown.RNA interfering technology is a new biologic technique which induces the sequence-specific message RNA degradation to posttranscriptional gene silence. This phenomenon is a kind of mechanism against invasion outside which widely exists in nature and contribute to stabilize the genome. Because of its specificity of rejecting and closing gene expression, RNAi is widely applied to explore gene function and malignant tumor therapy. Hence, in this study, RNA interfering technology was specifically utilized to knock down RPS15A expression in leukemia cells and we study the change of its functional and phenotypic information to further explore the molecular mechanism of leukemia caused by RPS15A.First, we construct RPS15A gene knockdown and overexpression vector, package into virus particles and infect human leukemia cell line U937. The expression level of RPS15A was analyzed in leukemia cell line U937 by quantitative polymerase chain reaction and western blot analysis to verify the inhibition efficiency. Moreover, cell viability was measured by methylthiazoletetrazolium assay. In addition, cell cycle distribution and apoptosis were investigated by flow cytometry. We observed the influence of cell proliferation, apoptosis and the distribution of the cycle after RPS15A silencing. The results showed that the mRNA and protein level of RPS15A gene were down-regulated in leukemia cells after lentivirus infection. Lentivirus mediated knockdown of RPS15A strongly reduced the proliferation and clone formation ability. After RPS15A silencing, cell cycle was arrested in G0/G1 phase and apoptotic cells were significantly increased by flow cytometry analysis.Taken together, RPS15A has important influences on the leukemia cell proliferation. These results indicated that knockdown of RPS15A by RNAi could be an effective therapeutic approach for the treatment of leukemia.