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Biology subjects

Sajwan, S.

Publications and source records attributed to Sajwan, S..

3 recordsLinked to original sources

Oncogenic ERK signaling represses chaperone-mediated autophagy through transcriptional control of LAMP-2A

Chaperone-mediated autophagy (CMA) is a selective lysosomal degradation pathway governed by the rate-limiting receptor LAMP-2A and increasingly implicated in cancer. However, the oncogenic circuits that enforce CMA repression and whether this state is therapeutically reversible remain unclear. Here, we developed a quantitative bioluminescence-based reporter to measure CMA activity in human cancer cells and combined parallel chemical and genome-scale CRISPR-Cas9 screens to define regulatory pathways. The chemical screen identified GSK1059615 as a CMA-restoring compound that increased LAMP-2A transcription and protein abundance in vitro and in vivo. In parallel, the CRISPR screen revealed ERK signaling as a pathway-level suppressor of CMA. Genetic or pharmacologic ERK inhibition de-repressed LAMP-2A expression, while integrated modulation of ERK, PI3K-AKT, and p38 signaling coordinated transcriptional induction and stabilization of LAMP-2A. Transcriptomic analyses further implicated FOXO1/FOXP1-driven programs in LAMP-2A regulation. Together, these findings position CMA as an integrated output of oncogenic signaling networks and establish a mechanistic framework for restoring CMA activity in defined cancer contexts.

cell biology↗

A Non-Transcriptional Mitotic Function of POU/Oct Factors Ensures Spindle Stability and Chromosome Segregation

POU/Oct transcription factors are critical regulators of cellular processes, including proliferation, cell fate determination, and cancer. Despite their importance, the specific molecular mechanisms by which they influence cell division remain largely unclear. Here, we show that Nub/Pdm1, a Drosophila homolog of human POU2F1/Oct1, is essential for accurate mitotic progression in a non-transcriptional manner. Live imaging and immunostaining in Drosophila embryos reveal that its depletion leads to disorganized spindles, aberrant chromosome segregation and delayed mitotic progression. Similarly, reduction of POU2F1/Oct1 in live human cells caused disorganized mitotic spindles and spindle collapse. Nub/Pdm1 is enriched within the mitotic spindles and this recruitment is independent of its sequence-specific DNA binding. Instead, it depends on the integrity of spindle microtubules and is regulated by mitosis-related motor proteins, and kinases. Our findings identify both fly Nub/Pdm1 and human Oct1 as important regulators of mitotic progression, acting to maintain spindle stability and proper elongation. The non-transcriptional mitotic role of Nub/Pdm1 reveals a previously unrecognized mechanism of POU/Oct proteins and provides new insight into their potential oncogenic properties. Highlights- Nub/Pdm1 is vital for accurate mitotic progression in a non-transcriptional manner - Nub/Pdm1 preserves spindle integrity during rapid syncytial nuclear divisions - Nub/Pdm1 spindle enrichment depends on mitotic factors and intact microtubules - Nub and human Oct1 ensure proper chromosome segregation

cell biology↗

Catalytic-dependent and independent functions of the histone acetyltransferase CBP promote pioneer factor-mediated zygotic genome activation

Immediately after fertilization the genome is transcriptionally quiescent. Maternally encoded pioneer transcription factors reprogram the chromatin state and facilitate the transcription of the zygotic genome. In Drosophila, transcription is initiated by the pioneer factor Zelda. While Zelda-occupied sites are enriched with histone acetylation, a post-translational mark associated with active cis-regulatory regions, the functional relationship between Zelda and histone acetylation in zygotic genome activation remained unclear. We show that Zelda-mediated recruitment of the histone acetyltransferase CBP is essential for zygotic transcription. CBP catalytic activity is necessary for release of RNA Polymerase II (Pol II) into transcription elongation and for embryonic development. However, CBP also activates zygotic transcription independent of acetylation through Pol II recruitment. Neither acetylation nor CBP are required for the pioneering function of Zelda. Our data suggest that pioneer factor-mediated recruitment of CBP is a conserved mechanism required to activate zygotic transcription but that this role is separable from the function of pioneer factors in restructuring chromatin accessibility.

developmental biology↗