Radhakrishnan, S. K. | Search bioRxiv

bioRxiv2018

Proteotoxic stress-induced Nrf1 transcriptional program requires a functional TIP60 complex

In response to inhibition of the cellular proteasome, the transcription factor Nrf1 (also called NFE2L1) induces transcription of proteasome subunit genes resulting in the restoration of proteasome activity and thus enabling the cells to mitigate the proteotoxic stress. To identify novel regulators of Nrf1, we performed an RNA interference screen and discovered that the AAA+ ATPase RUVBL1 is necessary for its transcriptional activity. Given that RUVBL1 is part of different multi-subunit complexes that play key roles in transcription, we dissected this phenomenon further and found that the TIP60 chromatin regulatory complex is essential for Nrf1-dependent transcription of proteasome genes. Consistent with these observations, Nrf1, RUVBL1, and TIP60 proteins were co-recruited to the promoter regions of proteasome genes after proteasome inhibitor treatments. More importantly, depletion of RUVBL1 or TIP60 in various cancer cells sensitized them to cell death induced by proteasome inhibition. Our study provides a framework for manipulating the Nrf1-TIP60 axis to alter proteasome function in various human diseases including cancer.

molecular biology↗

bioRxiv2018

Sensory domain of the cell cycle kinase CckA in Caulobacter crescentus regulates the differential DNA binding activity of the master regulator CtrA

Sophisticated signaling mechanisms allow bacterial cells to cope with environmental and intracellular challenges. Activation of specific pathways facilitates the cells to overcome cellular damage and thereby warrant integrity. Here we demonstrate the pliability of the CckA-CtrA two component signaling system in the freshwater bacterium, Caulobacter crescentus. Our forward genetic screen to analyse suppressor mutations that can negate the chromosome segregation block induced by the topoisomerase IV inhibitor, NstA, yielded various point mutations in the cell cycle histidine kinase, CckA. Notably, we identified a point mutation in the PAS-B domain of CckA, which resulted in increased levels of phosphorylated CtrA (CtrA[~]P), the master cell cycle regulator. Surprisingly, this increase in CtrA[~]P levels did not translate into a genome-wide increase in the DNA occupancy of CtrA, but specifically enriched its affinity to the chromosomal origin of replication, Cori, and a very small sub-set of CtrA regulated promoters. We show that through this enhanced binding of CtrA to the Cori, cells are able to overcome the toxic defects rendered by stable NstA through a possible slow down in the chromosome cycle. Taken together, our work opens up an unexplored and intriguing aspect of the CckA-CtrA signal transduction pathway. The distinctive DNA binding nature of CtrA and its regulation by CckA might also be crucial for pathogenesis because of the highly conserved nature of CckA-CtrA pathway in alphaproteobacteria.

microbiology↗