Haploinsufficiency for p190B RhoGAP inhibits MMTV-Neu tumor progression.
BACKGROUND
Rho signaling regulates key cellular processes including proliferation, survival, and migration, and it has been implicated in the development of many types of cancer including breast cancer. P190B Rho GTPase activating protein (RhoGAP) functions as a major inhibitor of the Rho GTPases. P190B is required for mammary gland morphogenesis, and overexpression of p190B in the mammary gland induces hyperplastic lesions. Hence, we hypothesized that p190B may play a pivotal role in mammary tumorigenesis.


METHODS
To investigate the effects of loss of p190B function on mammary tumor progression, p190B heterozygous mice were crossed with an MMTV-Neu breast cancer model. Effects of p190B deficiency on tumor latency, multiplicity, growth, preneoplastic progression and metastasis were evaluated. To investigate potential differences in tumor angiogenesis between the two groups, immunohistochemistry to detect von Willebrand factor was performed and quantified. To examine gene expression of potential mediators of the angiogenic switch, an angiogenesis PCR array was utilized and results were confirmed using immunohistochemistry. Finally, reciprocal transplantation of tumor fragments was performed to determine the impact of stromal deficiency of p190B on tumor angiogenesis.


RESULTS
P190B deficiency reduced tumor penetrance (53% of p190B+/-Neu mice vs. 100% of p190B+/+Neu mice formed tumors) and markedly delayed tumor onset by an average of 46 weeks. Tumor multiplicity was also decreased, but an increase in the number of preneoplastic lesions was detected indicating that p190B deficiency inhibited preneoplastic progression. Angiogenesis was decreased in the p190B heterozygous tumors, and expression of a potent angiogenic inhibitor, thrombospondin-1, was elevated in p190B+/-Neu mammary glands. Transplantation of p190B+/-Neu tumor fragments into wild-type recipients restored tumor angiogenesis. Strikingly, p190B+/+Neu tumor fragments were unable to grow when transplanted into p190B+/-Neu recipients.


CONCLUSIONS
These data suggest that p190B haploinsufficiency in the epithelium inhibits MMTV-Neu tumor initiation. Furthermore, p190B deficiency in the vasculature is responsible, in part, for the inhibition of MMTV-Neu tumor progression.
Heckman-Stoddard
Brandy M
BM
Department of Molecular and Cellular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA. bheckmanstoddard@gmail.com
Vargo-Gogola
Tracy
T
McHenry
Peter R
PR
Jiang
Vivian
V
Herrick
Matthew P
MP
Hilsenbeck
Susan G
SG
Settleman
Jeffrey
J
Rosen
Jeffrey M
JM
D000230:Adenocarcinoma / Q000098:blood supply / Q000201:enzymology / Q000235:genetics* / Q000473:pathology; D000818:Animals; D003433:Crosses, Genetic; D018450:Disease Progression; D004847:Epithelial Cells / Q000378:metabolism / Q000473:pathology; D005260:Female; D020690:GTPase-Activating Proteins / Q000172:deficiency* / Q000235:genetics / Q000502:physiology; D006579:Heterozygote; D008325:Mammary Neoplasms, Experimental / Q000098:blood supply / Q000201:enzymology / Q000235:genetics* / Q000473:pathology / Q000821:virology; D008324:Mammary Tumor Virus, Mouse; D051379:Mice; D008817:Mice, Mutant Strains; D016513:Mice, SCID; D009363:Neoplasm Proteins / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D009368:Neoplasm Transplantation; D009389:Neovascularization, Pathologic / Q000235:genetics / Q000473:pathology; D018719:Erb-b2 Receptor Tyrosine Kinases; D015398:Signal Transduction; D017154:Stromal Cells / Q000378:metabolism / Q000473:pathology; D019700:Thrombospondin 1 / Q000096:biosynthesis / Q000235:genetics
D020690:GTPase-Activating Proteins; D009363:Neoplasm Proteins; D018719:Erb-b2 Receptor Tyrosine Kinases; D019700:Thrombospondin 1; C513042:Arhgap5 protein, mouse; C524056:Erbb2 protein, mouse
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