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LTK is an ER-resident receptor tyrosine kinase that regulates secretion.

ABSTRACT: The endoplasmic reticulum (ER) is a key regulator of cellular proteostasis because it controls folding, sorting, and degradation of secretory proteins. Much has been learned about how environmentally triggered signaling pathways regulate ER function, but only little is known about local signaling at the ER. The identification of ER-resident signaling molecules will help gain a deeper understanding of the regulation of ER function and thus of proteostasis. Here, we show that leukocyte tyrosine kinase (LTK) is an ER-resident receptor tyrosine kinase. Depletion of LTK as well as its pharmacologic inhibition reduces the number of ER exit sites and slows ER-to-Golgi transport. Furthermore, we show that LTK interacts with and phosphorylates Sec12. Expression of a phosphoablating mutant of Sec12 reduces the efficiency of ER export. Thus, LTK-to-Sec12 signaling represents the first example of an ER-resident signaling module with the potential to regulate proteostasis.

SUBMITTER: Centonze FG

PROVIDER: S-EPMC6683734 | biostudies-literature | 2019 Aug

REPOSITORIES: biostudies-literature

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LTK is an ER-resident receptor tyrosine kinase that regulates secretion.

Centonze Federica G FG Reiterer Veronika V Nalbach Karsten K Saito Kota K Pawlowski Krzysztof K Behrends Christian C Farhan Hesso H

The Journal of cell biology 20190621 8

The endoplasmic reticulum (ER) is a key regulator of cellular proteostasis because it controls folding, sorting, and degradation of secretory proteins. Much has been learned about how environmentally triggered signaling pathways regulate ER function, but only little is known about local signaling at the ER. The identification of ER-resident signaling molecules will help gain a deeper understanding of the regulation of ER function and thus of proteostasis. Here, we show that leukocyte tyrosine ki ...[more]

PMID: 31227593

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Project description:NF?B signaling is of paramount importance in the regulation of apoptosis, proliferation, and inflammatory responses during human development and homeostasis, as well as in many human cancers. Receptor Tyrosine Kinases (RTKs), including the Fibroblast Growth Factor Receptors (FGFRs) are also important in development and disease. However, a direct relationship between growth factor signaling pathways and NF?B activation has not been previously described, although FGFs have been known to antagonize TNF?-induced apoptosis.Here, we demonstrate an interaction between FGFR4 and IKK? (Inhibitor of NF?B Kinase ? subunit), an essential component in the NF?B pathway. This novel interaction was identified utilizing a yeast two-hybrid screen [1] and confirmed by coimmunoprecipitation and mass spectrometry analysis. We demonstrate tyrosine phosphorylation of IKK? in the presence of activated FGFR4, but not kinase-dead FGFR4. Following stimulation by TNF? (Tumor Necrosis Factor ?) to activate NF?B pathways, FGFR4 activation results in significant inhibition of NF?B signaling as measured by decreased nuclear NF?B localization, by reduced NF?B transcriptional activation in electophoretic mobility shift assays, and by inhibition of IKK? kinase activity towards the substrate GST-I?B? in in vitro assays. FGF19 stimulation of endogenous FGFR4 in TNF?-treated DU145 prostate cancer cells also leads to a decrease in IKK? activity, concomitant reduction in NF?B nuclear localization, and reduced apoptosis. Microarray analysis demonstrates that FGF19 + TNF? treatment of DU145 cells, in comparison with TNF? alone, favors proliferative genes while downregulating genes involved in apoptotic responses and NF?B signaling.These results identify a compelling link between FGFR4 signaling and the NF?B pathway, and reveal that FGFR4 activation leads to a negative effect on NF?B signaling including an inhibitory effect on proapoptotic signaling. We anticipate that this interaction between an RTK and a component of NF?B signaling will not be limited to FGFR4 alone.

Dataset Information

LTK is an ER-resident receptor tyrosine kinase that regulates secretion.

Publications

LTK is an ER-resident receptor tyrosine kinase that regulates secretion.

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