Genomic structure of the human b-PIX gene and its alteration in gastric cancer Zhong-you Li a,b , You-jie Wang a , Jian-ping Song a , Hideki Kataoka a , Shigeto Yoshii a , Chang-ming Gao b , Ya-ping Wang b , Jian-nong Zhou b , Satoshi Ota a , Masamitsu Tanaka a , Haruhiko Sugimura a, * a First Department of Pathology, Hamamatsu University School of Medicine, 1-20-1, Handayama, Hamamatsu, 431-3192, Japan b Department of Molecular Oncology, Jiangsu Institute of Cancer Research, Nanjing, 210009, People’s Republic of China Received 14 August 2001; received in revised form 28 September 2001; accepted 1 October 2001 Abstract b-PIX, a newly identified p21-activated kinase (PAK)-interacting exchange factors (PIX), encodes a guanine nucleotide exchange factor for Rho guanosine triphosphatases. Characterization of b-PIX gene was performed using the BAC Library method. The b-PIX gene has 17 exons and an A/T polymorphism at the 32nd base upstream of the intron/exon junction of exon 7. The frequencies of genotypes A/T, A/A and T/T were 23.6% (13/55), 72.7% (40/55) and 3.6% (2/55), respectively; these frequencies are in Hardy–Weinberg equilibrium. Two out of 14 informative tumors (14.3%) were shown to have lost their heterozygosity at this locus, but no mutations in the remaining alleles were detected. In addition, we examined the gene- expression profile in another set of 30 gastric samples, but no significant over-expression of either the b-PIX gene or the a-PIX gene was found. Though the b-PIX gene has been speculated to potentially have tumor-related biological characteristics, the findings of the present study suggest that the involvement of b-PIX gene in human gastric carcinogenesis is minimal. q 2002 Elsevier Science Ireland Ltd. All rights reserved. Keywords: p21-Activated kinase-interacting exchange factors; Gastric cancer; Loss of heterozygosity; Polymorphism; Genomic structure; Gene expression 1. Introduction Members of the p21-activated kinase (PAK) family of serine/threonine kinases serve as targets for the small guanosine triphosphate- (GTP)-binding proteins Cdc42 and Rac and have been implicated in a wide range of biological activities, such as cytos- keletal architecture and gene expression [1–3], this implies that PAK and PAK-related molecules may ultimately be linked to various pathological states, including carcinogenesis. A recently identified guanine nucleotide exchange factor (GEF), one of several PAK-interacting exchange factors (PIX), contains several domains that could contribute to the cellular localization of the molecule as well as protein–protein and protein–lipid interactions [4–6]. This molecule may mediate the recruitment of PAK into focal adhesions [4,5]. Some experiments have already shown that PAK1–PIX complex is recruited to appropriate sites upon activation and that PIX is required for Rho family GTPase activation upstream Cancer Letters 177 (2002) 203–208 0304-3835/02/$ - see front matter q 2002 Elsevier Science Ireland Ltd. All rights reserved. PII: S0304-3835(01)00798-4 www.elsevier.com/locate/canlet * Corresponding author. Tel.: 181-53-435-2220; fax: 181-53- 435-2225. E-mail address: hsugimur@hama-med.ac.jp (H. Sugimura).