Biomedical subjects

Ketu Mishra-Gorur

Publications and source records attributed to Ketu Mishra-Gorur.

4 recordsLinked to original sources

PubMed2025

Dysregulation of mTOR signalling is a converging mechanism in lissencephaly.

Cerebral cortex development in humans is a highly complex and orchestrated process that is under tight genetic regulation. Rare mutations that alter gene expression or function can disrupt the structure of the cerebral cortex, resulting in a range of neurological conditions1. Lissencephaly ('smooth brain') spectrum disorders comprise a group of rare, genetically heterogeneous congenital brain malformations commonly associated with epilepsy and intellectual disability2. However, the molecular mechanisms underlying disease pathogenesis remain unknown. Here we establish hypoactivity of the mTOR pathway as a clinically relevant molecular mechanism in lissencephaly spectrum disorders. We characterized two types of cerebral organoid derived from individuals with genetically distinct lissencephalies with a recessive mutation in p53-induced death domain protein 1 (PIDD1) or a heterozygous chromosome 17p13.3 microdeletion leading to Miller-Dieker lissencephaly syndrome (MDLS). PIDD1-mutant organoids and MDLS organoids recapitulated the thickened cortex typical of human lissencephaly and demonstrated dysregulation of protein translation, metabolism and the mTOR pathway. A brain-selective activator of mTOR complex 1 prevented and reversed cellular and molecular defects in the lissencephaly organoids. Our findings show that a converging molecular mechanism contributes to two genetically distinct lissencephaly spectrum disorders.

Humans↗

PubMed2002

Down-regulation of Delta by proteolytic processing.

Notch signaling regulates cell fate decisions during development through local cell interactions. Signaling is triggered by the interaction of the Notch receptor with its transmembrane ligands expressed on adjacent cells. Recent studies suggest that Delta is cleaved to release an extracellular fragment, DlEC, by a mechanism that involves the activity of the metalloprotease Kuzbanian; however, the functional significance of that cleavage remains controversial. Using independent functional assays in vitro and in vivo, we examined the biological activity of purified soluble Delta forms and conclude that Delta cleavage is an important down-regulating event in Notch signaling. The data support a model whereby Delta inactivation is essential for providing the critical ligand/receptor expression differential between neighboring cells in order to distinguish the signaling versus the receiving partner.

Animals↗

PubMed2002

The S18 ribosomal protein is a putative substrate for Ca2+/calmodulin-activated protein kinase II.

The delta-isoform of Ca(2+)/calmodulin-activated protein kinase II (CaMK II) is abundantly expressed in vascular smooth muscle, but relatively little is known about its regulation or its potential cellular substrates. There are few, if any, known substrates of CaMK II that are physiologically relevant in vascular smooth muscle cells. Studies presented earlier (Mishra-Gorur, K., Singer, H. A., and Castellot, J. J., Jr. (2002) Am. J. Pathol., in press) by our laboratory show an inhibitory effect of heparin on CaMK II phosphorylation and activity. During these studies we observed the specific co-immunoprecipitation of a 20-kDa protein with CaMK II. Purification and sequence analysis indicate that this protein is the S18 protein of the 40 S ribosome. S18 was found to be abundantly phosphorylated in response to serum treatment, and this effect was strongly inhibited by heparin. In addition, KN-93, a specific CaMK II inhibitor, blocks S18 phosphorylation in vascular smooth muscle cells; a concomitant 24% reduction in protein synthesis was observed. Taken together these data support the idea that S18 could be a novel substrate for CaMK II, thus providing a potential link between Ca(2+)-mobilizing agents and protein translation.

Amino Acid Sequence↗

PubMed2002

Heparin inhibits phosphorylation and autonomous activity of Ca(2+)/calmodulin-dependent protein kinase II in vascular smooth muscle cells.

Vascular smooth muscle cell (VSMC) hyperproliferation is a characteristic feature of both atherosclerosis and restenosis seen after vascular surgery. A number of studies have shown that heparin inhibits VSMC proliferation in vivo and in culture. To test our hypothesis that heparin mediates its antiproliferative effect by altering Ca(2+) regulated pathways involved in mitogenic signaling in VSMC, we analyzed the effect of heparin on multifunctional Ca(2+)/calmodulin dependent protein kinase II (CaM kinase II) which is abundantly expressed in VSMC. Using activity assays, radioactive labeling, and immunoprecipitation it was found that heparin inhibits the overall phosphorylation of the delta-subunit of CaM kinase II which is consistent with inhibition of autophosphorylation-dependent, Ca(2+)/calmodulin-independent CaM kinase II activity. This effect was less evident in heparin-resistant cells, consistent with a role for CaM kinase II in mediating the antiproliferative effect of heparin. Finally, the effects of pharmacological inhibitors of phosphatases like okadaic acid, calyculin, and tautomycin suggest that heparin inhibits CaM kinase II phosphorylation by activating protein phosphatases 1 and 2A. These findings support the hypothesis that alterations in calcium-mediated mitogenic signaling pathways may be involved in the antiproliferative mechanism of action of heparin.

Animals↗