Highlights d Autophagy initiation is repressed during mitosis, even during nutrient deprivation d RAPTOR phosphorylation in mitosis prevents mTORC1 localization to lysosomes d mTORC1 is inhibited during mitosis d CDK1 phosphorylates autophagy regulators at mTORC1 sites to repress autophagy

The RAS-regulated RAF-MEK1/2-ERK1/2 signaling pathway is frequently deregulated in cancer due to activating mutations of growth factor receptors, RAS or BRAF. Both RAF and MEK1/2 inhibitors are clinically approved and various ERK1/2 inhibitors (ERKi) are currently undergoing clinical trials. To date, ERKi display two distinct mechanisms of action (MoA): catalytic ERKi solely inhibit ERK1/2 catalytic activity, whereas dual mechanism ERKi additionally prevents the activating phosphorylation of ERK1/2 at its T-E-Y motif by MEK1/2. These differences may impart significant differences in biological activity because T-E-Y phosphorylation is the signal for nuclear entry of ERK1/2, allowing them to access many key transcription factor targets.Here, we characterized the MoA of five ERKi and examined their functional consequences in terms of ERK1/2 signaling, gene expression, and antiproliferative efficacy. We demonstrate that catalytic ERKi promote a striking nuclear accumulation of p-ERK1/2 in KRAS-mutant cell lines. In contrast, dualmechanism ERKi exploits a distinct binding mode to block ERK1/2 phosphorylation by MEK1/2, exhibit superior potency, and prevent the nuclear accumulation of ERK1/2. Consequently, dual-mechanism ERKi exhibit more durable pathway inhibition and enhanced suppression of ERK1/2-dependent gene expression compared with catalytic ERKi, resulting in increased efficacy across BRAF-and RAS-mutant cell lines.

Class I phosphoinositide 3-kinase (PI3K) and mechanistic target of rapamycin complex 1 (mTORC1) signalling is inhibited during mitosis, so that autophagy and cap-dependent translation are uncoupled from nutrient availability.During mitosis, cyclin-dependent kinase 1 (CDK1) promotes phosphorylation of RAPTOR, causing dissociation of mTORC1 from lysosomes, thereby inhibiting it. CDK1 substitutes for inhibited mTORC1 by phosphorylating ATG13, ULK1, and ATG14 at canonical mTOR sites and also phosphorylates VPS34. In addition, WIPI2 undergoes ubiquitination and degradation. This ensures a system-wide repression of autophagy during mitosis.CDK1 also takes over the mTORC1dependent phosphorylation of eukaryotic translation initiation factor 4E-binding proteins (4E-BPs) to maintain cap-dependent translation of 5′ terminal oligopyrimidine (TOP) mRNAs.The ULK1 complex has roles in mitotic division, which may be dependent on its phosphorylation by CDK1. There is ongoing debate as to whether this is linked to ULK1's role in autophagy or by phosphorylating substrates such as Mad1.

Development of cervical squamous cell carcinoma requires increased expression of the major high-risk human-papillomavirus (HPV) oncogenes E6 and E7 in basal cervical epithelial cells. We used a systems biology approach to identify host transcriptional networks in such cells and study the concentration-dependent changes produced by HPV16-E6 and -E7 oncoproteins. We investigated sample sets derived from the W12 model of cervical neoplastic progression, for which high quality phenotype/genotype data were available. We defined a gene co-expression matrix containing a small number of highly-connected hub nodes that controlled large numbers of downstream genes (regulons), indicating the scale-free nature of host gene co-expression in W12. We identified a small number of ‘master regulators’ for which downstream effector genes were significantly associated with protein levels of HPV16 E6 (n = 7) or HPV16 E7 (n = 5). We validated our data by depleting E6/E7 in relevant cells and by functional analysis of selected genes in vitro. We conclude that the network of transcriptional interactions in HPV16-infected basal-type cervical epithelium is regulated in a concentration-dependent manner by E6/E7, via a limited number of central master-regulators. These effects are likely to be significant in cervical carcinogenesis, where there is competitive selection of cells with elevated expression of virus oncoproteins.

For the last two decades there has been wide ranging debate about the status of macroautophagy during mitosis. Because metazoan cells undergo an "open" mitosis in which the nuclear envelope breaks down, it has been proposed that macroautophagy must be inhibited to maintain genome integrity. While many studies have agreed that the number of autophagosomes is greatly reduced in cells undergoing mitosis, there has been no consensus on whether this reflects decreased autophagosome synthesis or increased autophagosome degradation. Reviewing the literature we were concerned that many studies relied too heavily on autophagy assays that were simply not appropriate for a relatively brief event such as mitosis. Using highly dynamic omegasome markers we have recently shown unequivocally that autophagosome synthesis is repressed at the onset of mitosis and is restored once cell division is complete. This is accomplished by CDK1, the master regulator of mitosis, taking over the function of MTORC1, to ensure autophagy is repressed during mitosis.