Biology subjects

Ghosh, M. K.

Publications and source records attributed to Ghosh, M. K..

3 recordsLinked to original sources

bioRxiv2021

Identification and validation of E3 ubiquitin ligase XIAP as a novel substrate of deubiquitinase USP7 (HAUSP) - Implication towards oncogenesis

The induction of apoptosis upon USP7 (HAUSP) inhibition is established in cancers that contain a wild-type p53 (p53Wt) through the USP7-Mdm2-p53 axis, but no clear explanation has yet been reported for the same to occur in cancers containing mutant 53 (p53Mut) or even p53 null (p53Null) systems. Instead of this USP7-Mdm2-p53 axis USP7 also works through an alternative new pathway identified in this study. Here in this study, we observed that the magnitude of apoptosis induction in response to USP7 inhibition was remarkably similar between cancer cells showing p53Null or p53Mut and those with p53Wt. Through a proteomics-based approach, we were able to identify XIAP as a novel interacting partner for USP7. XIAP is a potent and well-characterized member of the inhibitor of apoptosis proteins (IAPs), which function through caspase inhibition. We successfully identified USP7 as a positive regulator of XIAP at post-translational but not at its transcriptional level. Using molecular modelling coupled with domain deletion studies, we show that the first three Ubl domains in association with the catalytic domain of USP7 interact with the BIR2 and the linker region between BIR2 and BIR3 domains of XIAP. Modulation of expression and catalytic activity of USP7 in multiple type of cancer cell lines showed that USP7 stabilizes XIAP through its deubiquitinase activity. We have also observed that USP7 sensitizes cells against chemotherapeutic drugs through stabilization of XIAP. Thus, USP7 promotes tumorigenesis in multiple cancers, via stabilization of XIAP that results in apoptosis inhibition in caspase dependent pathway. Moreover, we observed that combinatorial inhibition of USP7 and XIAP can induce cellular apoptosis in a higher magnitude than their individual inhibition. Additionally, our results indicates that nanoformulated P5091 and P22077 showed higher potency for killing C6 cells in comparison to normal drugs. To the best of our knowledge, this is the first report on identification and validation of XIAP, a crucial E3 ubiquitin ligase, as a novel substrate of the deubiquitinase USP7 and they together involve in empowerment of the tumorigenic potential of cancer cells.

cancer biology↗

bioRxiv2021

Wnt/β-catenin signaling and p68 conjointly regulate CHIP in colorectal cancer

The differential expression pattern of Carboxy terminus of Hsc70 Interacting Protein (CHIP, alias STIP1 Homology and U-box Containing Protein 1 or STUB1) in cancers is associated with ubiquitination mediated degradation of its client proteins. Emerging evidences suggest its abundant expression of CHIP in colorectal cancer compared to normal tissues, but the mechanistic detail of this augmented expression pattern is unclear. The signature driver of canonical Wnt pathway, {beta}-catenin, and its co-activator RNA helicase p68, are also overexpressed in colorectal cancer. In this study, we describe a novel mechanism of Wnt/{beta}-catenin and p68 mediated transcriptional activation of CHIP gene leading to enhanced proliferation of colorectal cancer cells. Wnt3A treatment and pharmacological activation of canonical Wnt signaling pathway resulted in increased nuclear translocation of {beta}-catenin and elevated expression of CHIP. Likewise, overexpression and knockdown of {beta}-catenin and p68 upregulated and downregulated CHIP expression, respectively, at both mRNA and protein levels. After cloning CHIP promoter, the increased and decreased promoter activities of CHIP induced by overexpression and knockdown of either {beta}-catenin or p68 further confirmed transcriptional regulation of CHIP gene by Wnt/{beta}-catenin signaling cascade. p68 along with {beta}-catenin were found to occupy Transcription Factor 4 (TCF4) binding sites on endogenous CHIP promoter and regulate its transcription. Finally, enhanced cellular propagation and migration of colorectal cancer cells induced by Wnt/{beta}-catenin-p68-CHIP axis established the significance of this pathway in oncogenesis. To the best of our knowledge, this is the first report elucidating the mechanistic details of transcriptional regulation of CHIP (STUB1) gene expression.

cancer biology↗

bioRxiv2020

Recapitulating the frataxin activation mechanism in an engineered bacterial cysteine desulfurase supports the architectural switch model

Iron-sulfur (Fe-S) clusters have a key role in many biochemical processes and are essential for most life forms. Despite recent mechanistic advances in understanding the Fe-S cluster biosynthetic pathway, critical questions remain unresolved. Although human NFS1 and E. coli IscS share [~]60% sequence identity, NFS1 exhibits low activity and requires activation by the Friedreichs ataxia protein frataxin (FXN) for in vivo function. Surprisingly, structures of the human complex reveal three distinct quaternary structures with one form exhibiting the same subunit interactions as IscS. An architectural switch model has been proposed in which evolutionarily lost interactions between NFS1 subunits results in the formation of low-activity architectures; FXN binding compensates for these lost interactions and facilitates a subunit rearrangement to activate the complex. Here, we used a structure and evolution-guided approach to identify three conserved residues proposed to weaken interactions between NFS1 subunits and transplanted these amino acids into IscS. Compared to native IscS, the engineered variant had a 4000-fold weaker dimer interface and diminished activity that correlated with the absence of the second catalytic subunit. Remarkably, the addition of the FXN homolog to the engineered variant stimulated the decay of the Cys-quinonoid pyridoxal 5-phosphate intermediate, shifted IscS from the monomeric to dimeric form, and increased the cysteine desulfurase activity, reproducing results from the human system and supporting the architectural switch model. Overall, these studies indicate a weakening of the homodimeric interface was a key development during the evolution of the eukaryotic system and provide new insights into the role of FXN.

biochemistry↗