DLC-1 suppresses non-small cell lung cancer growth and invasion by RhoGAP-dependent and independent mechanisms.
Expression of the tumor suppressor deleted in liver cancer-1 (DLC-1) is lost in non-small cell lung (NSCLC) and other human carcinomas, and ectopic DLC-1 expression dramatically reduces proliferation and tumorigenicity. DLC-1 is a multi-domain protein that includes a Rho GTPase activating protein (RhoGAP) domain which has been hypothesized to be the basis of its tumor suppressive actions. To address the importance of the RhoGAP function of DLC-1 in tumor suppression, we performed biochemical and biological studies evaluating DLC-1 in NSCLC. Full-length DLC-1 exhibited strong GAP activity for RhoA as well as RhoB and RhoC, but only very limited activity for Cdc42 in vitro. In contrast, the isolated RhoGAP domain showed 5- to 20-fold enhanced activity for RhoA, RhoB, RhoC, and Cdc42. DLC-1 protein expression was absent in six of nine NSCLC cell lines. Restoration of DLC-1 expression in DLC-1-deficient NSCLC cell lines reduced RhoA activity, and experiments with a RhoA biosensor demonstrated that DLC-1 dramatically reduces RhoA activity at the leading edge of cellular protrusions. Furthermore, DLC-1 expression in NSCLC cell lines impaired both anchorage-dependent and -independent growth, as well as invasion in vitro. Surprisingly, we found that the anti-tumor activity of DLC-1 was due to both RhoGAP-dependent and -independent activities. Unlike the rat homologue p122RhoGAP, DLC-1 was not capable of activating the phospholipid hydrolysis activity of phospholipase C-delta1. Combined, these studies provide information on the mechanism of DLC-1 function and regulation, and further support the role of DLC-1 tumor suppression in NSCLC.
Healy
Kevin D
KD
Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, NC 27599-7295, USA.
Hodgson
Louis
L
Kim
Tai-Young
TY
Shutes
Adam
A
Maddileti
Savitri
S
Juliano
Rudolph L
RL
Hahn
Klaus M
KM
Harden
T Kendall
TK
Bang
Yung-Jue
YJ
Der
Channing J
CJ
D002289:Carcinoma, Non-Small-Cell Lung / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*; D002465:Cell Movement; D003094:Collagen / Q000378:metabolism; D017931:DNA Primers; D004338:Drug Combinations; D020690:GTPase-Activating Proteins; D015972:Gene Expression Regulation, Neoplastic; D016147:Genes, Tumor Suppressor / Q000502:physiology; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D006868:Hydrolysis; D007797:Laminin / Q000378:metabolism; D008175:Lung Neoplasms / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*; D009361:Neoplasm Invasiveness; D054803:Phospholipase C delta / Q000378:metabolism; D016133:Polymerase Chain Reaction; D011509:Proteoglycans / Q000378:metabolism; D014407:Tumor Cells, Cultured; D014410:Tumor Stem Cell Assay; D025521:Tumor Suppressor Proteins / Q000502:physiology*; D020741:rho GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D020742:rhoA GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*; D020743:rhoB GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*; D000075024:rhoC GTP-Binding Protein
C112352:DLC1 protein, human; D017931:DNA Primers; D004338:Drug Combinations; D020690:GTPase-Activating Proteins; D007797:Laminin; D011509:Proteoglycans; D025521:Tumor Suppressor Proteins; C059485:matrigel; D006160:Guanosine Triphosphate; D003094:Collagen; C518024:PLCD1 protein, human; D054803:Phospholipase C delta; C066690:RHOC protein, human; D020741:rho GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein; D020743:rhoB GTP-Binding Protein; D000075024:rhoC GTP-Binding Protein