STARD13

STARD13 serves as a Rho GTPase-activating protein (GAP), a type of protein that regulates members of the Rho family of GTPases.[7] It selectively activates RhoA and CDC42 and suppresses cell growth by inhibiting actin stress fiber assembly.[7]

The protein consists of an N-terminal sterile alpha motif (SAM) domain,[8] a serine-rich domain, a RhoGAP domain and at the C-terminus, a StAR-related lipid-transfer domain (START).

The protein was identified in part through its differential expression in cancers. A low level of STARD13 was observed in less differentiated hepatocellular carcinoma tissue with higher RhoA expression. A small patient study finds that the absence of STARD13 in hepatocellular carcinomas correlates with higher levels of RhoA and a poorer prognosis than patients with carcinomas that were STARD13-positive.[9]

Model organisms have been used in the study of STARD13 function. A conditional knockout mouse line, called Stard13^{tm1a(KOMP)Wtsi}[15][16] was generated as part of the International Knockout Mouse Consortium program — a high-throughput mutagenesis project to generate and distribute animal models of disease to interested scientists — at the Wellcome Trust Sanger Institute.[17][18][19]

Male and female animals underwent a standardized phenotypic screen to determine the effects of deletion.[13][20] Twenty four tests were carried out on mutant mice and two significant abnormalities were observed. Female homozygous mutants had an increased susceptibility to Citrobacter infection and displayed a decreased hematocrit and hemoglobin content.[13]

Another study of mice lacking STARD13, found it may promote blood vessel formation (angiogenesis), especially by tumor cells.[21] The promotion of angiogenesis with the loss of STARD13 occurs through the actions of RhoA.[21]