Battaglioni, S. | bioRxiv Science

bioRxiv2022

TORC1 phosphorylates and inhibits the ribosome preservation factor Stm1 to activate dormant ribosomes

Target of rapamycin complex 1 (TORC1) promotes biogenesis and inhibits degradation of ribosomes in response to nutrient availability. To ensure a basal supply of ribosomes, cells preserve a small pool of dormant ribosomes under nutrient-limited conditions. The regulation of dormant ribosomes is poorly characterized. Here, we show that upon inhibition of TORC1 by rapamycin or nitrogen starvation, Stm1 (suppressor of target of Myb protein 1) forms non-translating, dormant 80S ribosomes. Furthermore, Stm1-bound 80S ribosomes are protected from proteasomal degradation. Upon re-feeding, TORC1 directly phosphorylates and inhibits Stm1, thereby reactivating translation. Finally, SERBP1 (SERPINE1 mRNA binding protein), a mammalian ortholog of Stm1, forms dormant 80S ribosomes upon mTORC1 inhibition in mammalian cells. Thus, TORC1 regulates ribosomal dormancy in an evolutionarily conserved manner via a ribosome preservation factor.

molecular biology↗

bioRxiv2020

Coincidence detection of mitogenic signals via cytosolic pH regulates Cyclin D1 expression

Enhanced cell growth and proliferation are accompanied by profound changes in cellular metabolism. Originally identified as the Warburg effect in cancer, such metabolic changes are also common under physiological conditions and include increased fermentation and elevated cytosolic pH (pHc)1,2. However, how these changes contribute to enhanced cell growth and proliferation is unclear. Here, we demonstrate that elevated pHc specifically orchestrates an E2F-dependent transcriptional program to drive cell proliferation by promoting Cyclin D1 expression. pHc-dependent transcription of Cyclin D1 requires the transcription factors CREB1/ATF1 and ETS1 and the Histone Acetyltransferases p300/CBP. Interestingly, biochemical characterization revealed that the CREB1-p300/CBP interaction acts as a pH-sensor and coincidence detector linking different mitotic signals to Cyclin D1 transcription. We also show that elevated pHc contributes to increased Cyclin D1 expression in Malignant Pleural Mesotheliomas (MPMs) and renders them hypersensitive to pharmacological reduction of pHc. Taken together, these data demonstrate that elevated pHc is a critical cellular signal regulating G1 progression and provide a mechanism linking elevated pHc to oncogenic activation of Cyclin D1 in MPMs and possibly other Cyclin D1-dependent tumors. Thus, an increase of pHc may represent a functionally important, early event in the etiology of cancer amenable to therapeutic intervention.

cell biology↗