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Cell Biology International (2007) 31, 119–125 (Printed in Great Britain)

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Expression of PTEN and Akt phosphorylation in lipopolysaccharide-treated NIH3T3 cells

Hirohiko Okamura^a*, Kaya Yoshida^a, Eiko Sasaki^a, Lihong Qiu^a, Bruna Rabelo Amorim^a, Hiroyuki Morimoto^b and Tatsuji Haneji^a

^aDepartment of Histology and Oral Histology, Institute of Health Biosciences, The University of Tokushima Graduate School, 3-18-15 Kuramoto-cho, Tokushima 770-8504, Japan
^bDepartment of Oral and Maxillofacial Anatomy, Institute of Health Biosciences, The University of Tokushima Graduate School, Kuramoto, Tokushima 770-8504, Japan

Abstract

PTEN is a tumor suppressor gene encoding a phosphatase, and it negatively regulates cell survival mediated by the phosphoinositol 3-kinase (PI3-Kinase)-Akt pathway. To elucidate PTEN expression and its effect on the PI3-kinase-Akt pathway in fibroblasts and macrophages, we investigated the expression of PTEN and the phosphorylation status of Akt in NIH3T3 and RAW264.7 cells treated with LPS. Phosphorylation of Akt was induced by LPS treatment in a dose-dependent manner in RAW264.7 cells, but not in NIH3T3 cells. LPS induced the expression of PTEN in a dose and time-dependent manner in NIH3T3 cells (0–1μg/ml, 0–6h). However, LPS did not stimulate PTEN expression in RAW264.7 cells. These data indicate the existence of diverse mechanisms for PTEN expression and Akt activation in fibroblasts and macrophages. RNA interference using double-stranded RNA specific for the PTEN gene reduced both mRNA and protein levels of PTEN in NIH3T3 cells treated or not with LPS. The phosphorylation status of Akt in NIH3T3 cells stimulated with LPS did not change when the PTEN expression had been inhibited by RNA interference. The present results suggest that the up-regulation of PTEN expression by LPS is not involved in the activation of Akt in NIH3T3 cells. PTEN expression might be involved in the diverse inflammatory responses to LPS in fibroblasts and macrophages.

Key words: Akt, Fibroblast, Lipopolysaccharide, Phosphorylation, PTEN.

^*Corresponding author. Tel.: +81 88 633 7322; fax: +81 88 633 7342.

Received 15 February 2006/31 July 2006; accepted 14 September 2006