Biology subjects

Chakraborty, M. P.

Publications and source records attributed to Chakraborty, M. P..

4 recordsLinked to original sources

bioRxiv2026

Loss of PTPRB function remodels VEGFR1 activation in tumors overexpressing the receptor tyrosine kinase

The VEGF Receptor-1 (VEGFR1) is a deceptive receptor tyrosine kinase (RTK). In early embryonic development, VEGFR1 negatively regulates angiogenesis by acting like a decoy receptor. Ligand binding transiently phosphorylates the receptor and induces a weak activation, even at high receptor density. Yet, in multiple cancers, overexpression of VEGFR1 plays a central role in tumor vascularization and growth. Unlike many pro-oncogenic RTKs, extensive patient data analysis revealed no somatic mutation in VEGFR1 that may spontaneously activate the tyrosine kinase. The mechanism by which VEGFR1 is activated in cancers has remained an open question for more than two decades. Here, we evaluated the multi-omics profiles of VEGFR1 and its regulators in a pan-cancer database. We observed an inverse correlation between VEGFR1 and PTPRB phosphatase expression in KIRC patients and disease outcome. We observed that patients overexpressing VEGFR1 and deficient in PTPRB expression have a lower likelihood of survival. Using super-resolution single-cell imaging, we discovered that inhibiting PTPRB spontaneously activates VEGFR1 by inducing ligand-independent dimerization, possibly by shifting the equilibrium toward the active state. PTPRB inhibition induces sustained, ligand-dependent phosphorylation of VEGFR1, which may promote tumor vascularization. We conclude that a subtle phosphatase imbalance is fundamental in determining VEGFR1s role in pathological angiogenesis in tumors.

biochemistry↗

bioRxiv2025

Molecular Basis of Ionic Suppression of ZAP-70 Dependent T Cell Receptor Activation

Ionic imbalance in the tumor microenvironment alters the tumor-infiltrating T lymphocyte function. High extracellular K+ suppresses T cell function by negatively regulating T cell receptor (TCR) signaling. In contrast, elevated extracellular Na+ enhances T cell effector function by boosting the phosphorylation of TCR signaling modules. Here, we presented a mechanism explaining how the two monovalent cations differently regulate TCR function. At rest, high intracellular K+ uncouples allosteric recruitment of ZAP-70, a key signaling module, to the TCR complex. The formation of antigen TCR complex induces K+ efflux, causing spontaneous recruitment of ZAP-70 to the TCR. Increasing extracellular K+ perturbs K+ efflux and slows ZAP-70 recruitment to the TCR complex, even upon antigen binding. This leads to defects in T cell development and arthritis-like symptoms in juvenile mice. We conclude that K+ dynamics is integral to T cell ligand discrimination and fundamental to turning off the signaling during T cell quiescence.

immunology↗

bioRxiv2024

E41K Mutation Activates Brutons Tyrosine Kinase by Stabilizing an Inositol Hexakisphosphate Dependent Invisible Dimer

Brutons tyrosine kinase (BTK) regulates diverse cellular signaling of the innate and adaptive immune system in response to microbial pathogens. Downregulation or constitutive activation of BTK is reported in patients with autoimmune diseases or various B-cell leukemias. BTK is a multidomain protein tyrosine kinase that adopts an Src-like autoinhibited conformation maintained by the interaction between the kinase and PH-TH domains. The PH-TH domain plays a central role in regulating BTK function. The BTK is activated by binding to PIP3 at the plasma membrane upon stimulation by the B-cell receptor (BCR). The PIP3 binding allows dimerization of the PH-TH domain and subsequent transphosphorylation of the activation loop. Alternatively, a recent study shows that the multivalent T-cell-independent (TI) antigen induces BCR response by activating BTK independently of PIP3 binding. It was proposed that a transiently stable IP6-dependent PH-TH dimer may activate BTK during BCR activation by the TI antigens. However, no IP6-dependent PH-TH dimer has been identified yet. Here, we investigated a constitutively active PH-TH mutant (E41K) to determine if the elusive IP6-dependent PH-TH dimer exists. We showed that the constitutively active E41K mutation activates BTK by stabilizing the IP6-dependent PH-TH dimer. We observed that a downregulating mutation in the PH-TH domain (R28H) linked to X-linked agammaglobulinemia impairs BTK activation at the membrane and in the cytosol by preventing PH-TH dimerization. We conclude that the IP6 dynamically remodels the BTK active fraction between the membrane and cytoplasm. Stimulating with IP6 increases the cytosolic fraction of the activated BTK.

biochemistry↗

bioRxiv2023

Molecular basis of VEGFR1 autoinhibition at the plasma membrane

Ligand-independent activation of VEGFR is a hallmark in diabetes and several cancers. Like most RTKs, the VEGFR2, the primary VEGF receptor, is activated spontaneously at higher receptor concentrations. An exception is VEGFR1, which remains constitutively inactive in the basal state. Ligand stimulation transiently phosphorylates VEGFR1 and induces weak kinase activation in endothelial cells. Recent studies, however, suggest that VEGFR1 signaling is indispensable in regulating various physiological or pathological events, which is puzzling. Why VEGFR1 is differentially regulated is an open question. Here we elucidate a mechanism of juxtamembrane inhibition that shifts the equilibrium more to the inactive state, rendering VEGFR1 an inefficient kinase. Our data suggest that a combination of tyrosine phosphatase activity and JM inhibition suppress the basal phosphorylation of VEGFR1. We conclude that a subtle imbalance in phosphatase activation or removing juxtamembrane inhibition is sufficient to induce basal activation of VEGFR1 and remodel tyrosine phosphorylation to be sustained.

biochemistry↗