Deleted in liver cancer 1 (DLC1) utilizes a novel binding site for Tensin2 PTB domain interaction and is required for tumor-suppressive function.
BACKGROUND
Deleted in liver cancer 1 (DLC1) is a Rho GTPase-activating protein (RhoGAP) frequently deleted and underexpressed in hepatocellular carcinoma (HCC) as well as in other cancers. Recent independent studies have shown interaction of DLC1 with members of the tensin focal adhesion protein family in a Src Homology 2 (SH2) domain-dependent mechanism. DLC1 and tensins interact and co-localize to punctate structures at focal adhesions. However, the mechanisms underlying the interaction between DLC1 and various tensins remain controversial.


RESULTS
We used a co-immunoprecipitation assay to identify a previously undocumented binding site at 375-385 of DLC1 that predominantly interacted with the phosphotyrosine binding (PTB) domain of tensin2. DLC1-tensin2 interaction is completely abolished in a DLC1 mutant lacking this novel PTB binding site (DLC1DeltaPTB). However, as demonstrated by immunofluorescence and co-immunoprecipitation, neither the focal adhesion localization nor the interaction with tensin1 and C-terminal tensin-like (cten) were affected. Interestingly, the functional significance of this novel site was exhibited by the partial reduction of the RhoGAP activity, which, in turn, attenuated the growth-suppressive activity of DLC1 upon its removal from DLC1.


CONCLUSIONS
This study has provided new evidence that DLC1 also interacts with tensin2 in a PTB domain-dependent manner. In addition to properly localizing focal adhesions and preserving RhoGAP activity, DLC1 interaction with tensin2 through this novel focal adhesion binding site contributes to the growth-suppressive activity of DLC1.
Chan
Lo-Kong
LK
Department of Pathology, Liver Cancer and Hepatitis Research Laboratory and SH Ho Foundation Research Laboratories, The University of Hong Kong, Pokfulam, Hong Kong, China.
Ko
Frankie Chi Fat
FC
Ng
Irene Oi-Lin
IO
Yam
Judy Wai Ping
JW
D001665:Binding Sites; D015153:Blotting, Western; D002460:Cell Line; D049109:Cell Proliferation; D020690:GTPase-Activating Proteins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D047468:Immunoprecipitation; D008840:Microfilament Proteins / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D009154:Mutation / Q000235:genetics; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D017434:Protein Structure, Tertiary / Q000235:genetics / Q000502:physiology; D000070876:Tensins; D014410:Tumor Stem Cell Assay; D025521:Tumor Suppressor Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism / Q000502:physiology*
C112352:DLC1 protein, human; D020690:GTPase-Activating Proteins; D008840:Microfilament Proteins; D000070876:Tensins; D025521:Tumor Suppressor Proteins; C085379:rho GTPase-activating protein; C452816:TNS2 protein, human; D010744:Phosphoric Monoester Hydrolases