Kinase PIM1 promotes prostate cancer cell growth via c-Myc-RPS7-driven ribosomal stress.

Ribosomal stress is known to increase cancer risk, and we found that inhibition of kinase PIM1 attenuated PC3 cell growth and motility following the condensed cellular body and decreased protein translation in PIM1-inhibited cells. Additionally, PIM1 could regulate the expression of RPS7 through enhancing the protein stability of c-Myc, and enhancing RPS7 expression reversed the condensed cellular body and decreased protein translation resulted from PIM1 inhibition. Abstract Ribosomal stress is known to increase cancer risk; however, the molecular mechanism underlying its various effects on cancer remains unclear. To decipher this puzzle, we investigated the upstream signaling pathway that might be involved in promoting ribosomal stress that leads to tumor progression. Our results suggested that inhibition of kinase PIM1 attenuated PC3 cell growth and motility following the condensed cellular body and decreased protein translation in PIM1-inhibited cells. In addition, PIM1 was found to be a component of the small 40S ribosomal subunit and could regulate the expression of ribosomal small subunit protein 7 (RPS7). Our investigation also revealed that PIM1 enhanced the protein stability of c-Myc. Furthermore, a functional E-box motif was found upstream of the transcription start site in RPS7, and RPS7 has been proven to be a transcriptional target of c-Myc. Additionally, knocking down RPS7 dramatically reduced cell growth in vitro and in vivo, whereas enhancing RPS7 expression reversed the condensed cellular body and decreased protein translation resulted from PIM1 inhibition. Finally, biochemical recurrence-free survival and overall survival analysis indicated that the concomitant upregulation of PIM1 and RPS7 correlated with the worst prognosis of prostate cancer (PCa). Overall, our results demonstrated that kinase PIM1 promotes cell growth through c-Myc-RPS7-induced ribosomal stress in PCa. These findings substantially expanded our understanding on the molecular mechanism of PIM1-promoted abnormal ribosomal biosynthesis in tumorigenesis and tumor progression in PCa. Therapies that target molecules involved in PIM1-RPS7-induced ribosomal stress could provide a promising approach to treating PCa.