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Regulated cell cycle progression ensures homeostasis and prevents cancer. In proliferating cells, premature S phase entry is avoided by the E3 ubiquitin ligase anaphasepromoting complex/cyclosome (APC/C), although the APC/C substrates whose degradation restrains G1 -S progression are not fully known. The APC/C is also active in arrested cells that exited the cell cycle, but it is not clear whether APC/C maintains all types of arrest. Here, by expressing the APC/C inhibitor, EMI1, we show that APC/C activity is essential to prevent S phase entry in cells arrested by pharmacological cyclin-dependent kinases 4 and 6 (CDK4/6) inhibition (Palbociclib). Thus, active protein degradation is required for arrest alongside repressed cell cycle gene expression. The mechanism of rapid and robust arrest bypass from inhibiting APC/C involves CDKs acting in an atypical order to inactivate retinoblastoma-mediated E2F repression. Inactivating APC/C first causes mitotic cyclin B accumulation which then promotes cyclin A expression. We propose that cyclin A is the key substrate for maintaining arrest because APC/C-resistant cyclin A, but not cyclin B, is sufficient to induce S phase entry. Cells bypassing arrest from CDK4/6 inhibition initiate DNA replication with severely reduced origin licensing. The simultaneous accumulation of S phase licensing inhibitors, such as cyclin A and geminin, with G1 licensing activators disrupts the normal order of G1-S progression. As a result, DNA synthesis and cell proliferation are profoundly impaired. Our findings predict that cancers with elevated EMI1 expression will tend to escape CDK4/6 inhibition into a premature, underlicensed S phase and suffer enhanced genome instability. [ABSTRACT FROM AUTHOR]

STING is an innate immune sensor for immune surveillance of viral/bacterial infection and maintenance of an immune‐friendly microenvironment to prevent tumorigenesis. However, if and how STING exerts innate immunity‐independent function remains elusive. Here, the authors report that STING expression is increased in renal cell carcinoma (RCC) patients and governs tumor growth through non‐canonical innate immune signaling involving mitochondrial ROS maintenance and calcium homeostasis. Mitochondrial voltage‐dependent anion channel VDAC2 is identified as a new STING binding partner. STING depletion potentiates VDAC2/GRP75‐mediated MERC (mitochondria‐ER contact) formation to increase mitochondrial ROS/calcium levels, impairs mitochondria function, and suppresses mTORC1/S6K signaling leading to RCC growth retardation. STING interaction with VDAC2 occurs through STING‐C88/C91 palmitoylation and inhibiting STING palmitoyl‐transferases ZDHHCs by 2‐BP significantly impedes RCC cell growth alone or in combination with sorafenib. Together, these studies reveal an innate immunity‐independent function of STING in regulating mitochondrial function and growth in RCC, providing a rationale to target the STING/VDAC2 interaction in treating RCC. [ABSTRACT FROM AUTHOR]

Research shows that the mitogen-activated protein kinase (MAPK) Ste7 in the yeast Saccaromyces cerevisiae targets the MAPK target Kss1 during invasive growth. Experiments establish that Kss1 inhibits invasive growth when it is in its inactive form. Ste7 stimulates invasive growth by causing Kss1 to become active. Nitrogen plays a key role in MAPK-independent and MAPK-dependent growth patterns.

The cell division cycle must be strictly regulated during both development and adult maintenance, and efficient and well-controlled DNA replication is a key event in the cell cycle. DNA replication origins are prepared in G1 phase of the cell cycle in a process known as origin licensing which is essential for DNA replication initiation in the subsequent S phase. Appropriate origin licensing includes: (1) Licensing enough origins at adequate origin licensing speed to complete licensing before G1 phase ends; (2) Licensing origins such that they are well-distributed on all chromosomes. Both aspects of licensing are critical for replication efficiency and accuracy. In this minireview, we will discuss recent advances in defining how origin licensing speed and distribution are critical to ensure DNA replication completion and genome stability. [ABSTRACT FROM AUTHOR]

The ubiquitin-proteasome system is essential for cell cycle progression. Cyclin F is a cell cycle-regulated substrate adapter F-box protein for the Skp1, CUL1, and F-box protein (SCF) family of E3 ubiquitin ligases. Despite its importance in cell cycle progression, identifying cyclin F-bound SCF complex (SCFCyclin F) substrates has remained challenging. Since cyclin F overexpression rescues a yeast mutant in the cdc4 gene, we considered the possibility that other genes that genetically modify cdc4 mutant lethality could also encode cyclin F substrates. We identified the mitochondrial and cytosolic deacylating enzyme sirtuin 5 (SIRT5) as a novel cyclin F substrate. SIRT5 has been implicated in metabolic processes, but its connection to the cell cycle is not known. We show that cyclin F interacts with and controls the ubiquitination, abundance, and stability of SIRT5. We show SIRT5 knockout results in a diminished G1 population and a subsequent increase in both S and G2/M. Global proteomic analyses reveal cyclin-dependent kinase (CDK) signaling changes congruent with the cell cycle changes in SIRT5 knockout cells. Together, these data demonstrate that SIRT5 is regulated by cyclin F and suggest a connection between SIRT5, cell cycle regulation, and metabolism. [ABSTRACT FROM AUTHOR]