Protein Interaction Analysis of ST14 Domains and Their Point and Deletion Mutants

Shu Zheng,Kefeng Ding,Hanguang Hu,Weiting Ge,Lifeng Sun

doi:10.1074/jbc.m510687200

Abstract

ST14 (suppression of tumorigenicity 14) is a transmembrane serine protease that contains a serine protease catalytic (SP) domain, an SEA domain, two complement subcomponent C1r/s (CUB) domains, and four low density lipoprotein receptor class A domains. Glutathione S-transferase fusion proteins with SP, CUB, and low density lipoprotein receptor domains and their corresponding mutants were generated to analyze protein interactions with these domains. Modified glutathione S-transferase pull-down assays demonstrated the interaction between the SP domain and hepatocyte growth factor activator inhibitor-1. With the same method, a CUB domain-interacting protein was isolated and turned out to be the transmembrane protein with epidermal growth factor-like and two follistatin-like domains 1 (TMEFF1). Quantitative real time PCR revealed that the expression of the TMEFF1 gene was dependent on the transfection of the ST14 gene in the RKO cell line. Our results also suggested that ST14 and TMEFF1 were co-expressed in the human breast cancer cell line MCF7, human placenta, kidney, and liver tissues. Interestingly, these two genes were co-up-regulated in kidney tumors versus normal tissues, consistent with our results that showed the dependence of TMEFF1 expression on ST14 in RKO cells. Finally, homology modeling studies suggested that TMEFF1 might form a complex with ST14 by an interaction between epidermal growth factor and CUB domains.

Highlights

IntroductionST14 (suppression of tumorigenicity 14) is a multidomain transmembrane serine protease of the S1 trypsin-like protein family [1]
ST14 is a multidomain transmembrane serine protease of the S1 trypsin-like protein family [1]
Deletion of the second CUB domain would result in a poor activation of ST14 [11]

Summary

Introduction

ST14 (suppression of tumorigenicity 14) is a multidomain transmembrane serine protease of the S1 trypsin-like protein family [1]. It was first isolated as a novel matrix-degrading protease from human breast cancer cells by Shi et al [2]. By using subtractive hybridization to isolate genes that are highly expressed in normal intestinal mucosa but not expressed or expressed at a lower level in colon cancers [3], we obtained a clone that is identical to ST14. Takeuchi et al cloned ST14 from a human prostate cancer cell line and designated it the membrane type serine proteinase 1 [5]. ST14 is composed of an N-terminal transmembrane signal, a trypsinlike serine protease catalytic (SP) domain, a SEA domain, two tandem

Methods

Results

Conclusion