Depletion of Csk preferentially reduces the protein level of LynA in a Cbl-dependent manner in cancer cells

Takahisa Kuga,Masanari Taniguchi,Nobuyuki Yamagishi,Soujirou Hayashi,Naoto Yamaguchi,Yuka Yamane

doi:10.1038/s41598-020-64624-x

Takahisa Kuga, Masanari Taniguchi + Show 4 more

Open Access

https://doi.org/10.1038/s41598-020-64624-x

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Journal: Scientific Reports	Publication Date: May 6, 2020
Citations: 3	License type: open-access

Affiliation: Setsunan University, Chiba University

Abstract

There are eight human Src-family tyrosine kinases (SFKs). SFK members c-Src, c-Yes, Fyn, and Lyn are expressed in various cancer cells. SFK kinase activity is negatively regulated by Csk tyrosine kinase. Reduced activity of Csk causes aberrant activation of SFKs, which can be degraded by a compensatory mechanism depending on Cbl-family ubiquitin ligases. We herein investigated whether all SFK members are similarly downregulated by Cbl-family ubiquitin ligases in cancer cells lacking Csk activity. We performed Western blotting of multiple cancer cells knocked down for Csk and found that the protein levels of the 56 kDa isoform of Lyn (LynA), 53 kDa isoform of Lyn (LynB), c-Src, and Fyn, but not of c-Yes, were reduced by Csk depletion. Induction of c-Cbl protein levels was also observed in Csk-depleted cells. The reduction of LynA accompanying the depletion of Csk was significantly reversed by the knockdown for Cbls, whereas such significant recovery of LynB, c-Src, and Fyn was not observed. These results suggested that LynA is selectively downregulated by Cbls in cancer cells lacking Csk activity.

Highlights

There are eight human Src-family tyrosine kinases (SFKs)
In order to assess the effect of reduced activity of Csk on the protein levels of individual members of SFKs, we performed Western blotting of two types of cancer cells (HCT116 and HeLa S3 cells) transfected with small interfering RNA for Csk or control siRNA
Csk depletion did not affect the c-Yes protein levels in HeLa S3 and HCT116 cells (Fig. 1(c,d), Fig. S1b). These results suggested that LynA protein levels are preferentially repressed via Csk depletion in cancer cells

Summary

Introduction

SFK members c-Src, c-Yes, Fyn, and Lyn are expressed in various cancer cells. Reduced activity of Csk causes aberrant activation of SFKs, which can be degraded by a compensatory mechanism depending on Cbl-family ubiquitin ligases. We investigated whether all SFK members are downregulated by Cbl-family ubiquitin ligases in cancer cells lacking Csk activity. The reduction of LynA accompanying the depletion of Csk was significantly reversed by the knockdown for Cbls, whereas such significant recovery of LynB, c-Src, and Fyn was not observed These results suggested that LynA is selectively downregulated by Cbls in cancer cells lacking Csk activity. The Src-family tyrosine kinases (SFKs) are composed of eight members in humans: c-Src, c-Yes, Fyn, Lyn, Lck, Fgr, Hck and Blk. At least c-Src, Fyn, Lyn and Lck were reported to be substrates of Cbls[18,19,20,21,22,23]

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