With more than 160,000 new cases yearly, prostate cancer is males' most frequently diagnosed malignancy. Prostate cancer is still the third-leading cause of cancer-related mortality in males, despite often taking an indolent course [18]. One of the most frequent chromosomal abnormalities in prostate cancer development that overexpressed in PCa has been identified to be alterations of chromosome 8, including amplification at 8q24 containing the MYC oncogene [19]. The proto-oncogene MYC's transcript is often overexpressed in prostate cancer (PCa). Most advanced and metastatic castrate-resistant PCa cases also have elevated MYC protein abundance (mCRPC) [20].
The dysregulation of miRNA, a class of small endogenous regulatory RNAs with a size range of 20 to 22 nucleotides, is a critical factor in the development of tumors and is becoming more recognized as a possible cancer biomarker for early identification and treatment approaches [21]. Previous pancreatic and lung cancer studies have shown that miR-377 has decreased expression in tumor samples compared to controls [11, 22]. Additionally, it has been demonstrated that miR-377 expression is markedly downregulated in prostate cancer tissue. This downregulation is linked to the proliferation, apoptosis, migration, and invasion of metastatic prostate cancer cells [23].
As has shown the downregulation of miR-377 in prostate cancer cells [23, 24] we concentrated on its impact on prostate cancer cell lines in the current investigation. In this study, we demonstrated that the 3′-UTR of MYC is a functional target region for miR-377 in PC-3 and DU145 cells. According to data from luciferase reporters, the 3′-UTR of MYC is a target region for miR-377 in PC-3 and DU145 cells. There is much research showing that many human cancers, including lung tumors[25], hepatocellular carcinoma [26], osteosarcoma [27], clear cell renal cell carcinoma [28], glioblastoma [29], malignant melanoma [30], pancreatic cancer[11], and ovarian cancer [31], have been associated to miR-377 downregulation.
We also examined the levels of MYC mRNA expression in PC-3 and DU145 cells after miR-377 transfection to confirm that it could target this mRNA. Results indicated that miR-377 can decrease the MYC gene's mRNA expression level.
Moreover, the MYC gene has been shown to interact with other genes, such as BCL-2/Bax, PTEN, and CDK4. The anti-apoptotic protein encoded by the BCL-2 gene inhibits cell cycle progression [32]. MYC can upregulate BCL-2 expression, allowing malignant cells to avoid apoptosis and survive. BCL-2 gene expression is activated via MYC-mediated transcriptional activation. MYC gene overexpression can sometimes sensitize cancer cells to BCL-2 inhibitor-induced apoptosis. This is caused by disrupting the equilibrium between pro- and anti-apoptotic proteins, which activates the apoptotic pathway [33].
The BCL-2 protein controls apoptosis by permeating the mitochondrial membrane and is a potent inhibitor of the apoptotic process [34]. Overexpression of BCL-2 is observed in around 50% of all human malignancies. Additionally, BCL-2 and Bax (the pro-apoptotic component) form a heterodimer, and this contact eliminates Bax's pro-apoptotic properties [35]. Therefore, whether or not a cell undergoes apoptosis depends on the ratio of BCL-2/Bax. We found that miR-377 transfection significantly reduced the expression of BCL-2 protein in both PC-3 and DU145 prostate cancer cells. On the other hand, these cells' exposure to miR-377 boosted the expression of the Bax protein. This indicated that the Bax to BCL-2 ratio was changed in favor of apoptosis by the fall in MYC mRNA levels.
The PTEN gene functions as a suppressor of tumors by exerting a negative regulatory effect on the PI3K/AKT signaling pathway, which is known to play a crucial role in cellular growth and survival [36, 37]. The regulation of cell growth, proliferation, and survival in cancers is associated with the molecular interactions between the MYC gene and PTEN.
Overexpression of the MYC gene can result in the downregulation or loss of PTEN expression, activating the PI3K/AKT pathway, thereby facilitating cell growth and survival [38]. In this research, we showed that the transfection of miR-377 in prostate cancer cell lines causes a decrease in MYC expression, and the deduction of the mRNA level of MYC causes an increase in the mRNA level of PTEN, and consequently, survival and proliferation of prostate cancer cell lines decrease.
Cyclin-dependent kinase 4 (CDK4) regulates the cell cycle and interacts with the MYC gene in this process. It participates in the transition from the G1 to the S phase of the cell cycle [39]. Overexpression of the MYC gene can result in the upregulation of CDK4 expression, thereby facilitating cell cycle progression and cellular division [40]. In this study, we show that miR-377 transfection causes a stop in the cell cycle of prostate cancer cell lines due to the decrease in the expression level of MYC mRNA and, thus, the reduction in the expression level of CDK4 mRNA.
The effects of miR-377 on cell growth, apoptosis, and cell cycle were examined using an MTT test and flow cytometry. The findings showed that miR-377 significantly suppressed cell proliferation, induced apoptosis, stopped the cell cycle at G0/G1 phase, and inhibited cell migration in PC-3 and DU145 cells when compared to the control and scrambled miRNA, suggesting that miR-377 may have a function in preventing prostate cancer by targeting MYC 3’UTR. These findings were consistent with earlier research that showed miR-377 inhibits the proliferation of lung cancer[41], hepatocellular carcinoma [42], human osteosarcoma [43], glioblastoma [44], and pancreatic cancer cells [45] while promoting apoptosis in pancreatic cancer[45] and lung cancer cells[10].
According to all available information, miR-377 is essential for prostate and other cancer cells to stop proliferation, cell cycle, migration and undergo apoptosis. Questions remain about the matching molecules in the abovementioned processes and other miR-377 targets.