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J. Cell Biol.,
Volume 143, Number 3, November 2, 1998 861-873
Department of Biological Sciences, Wayne State University, Detroit, Michigan 48202
To investigate the role of nonreceptor protein tyrosine phosphatase 1B (PTP1B) in
1-integrin-
mediated adhesion and signaling, we transfected mouse
L cells with normal and catalytically inactive forms of
the phosphatase. Parental cells and cells expressing the
wild-type or mutant PTP1B were assayed for (a) adhesion, (b) spreading, (c) presence of focal adhesions and
stress fibers, and (d) tyrosine phosphorylation. Parental
cells and cells expressing wild-type PTP1B show similar
morphology, are able to attach and spread on fibronectin, and form focal adhesions and stress fibers. In contrast, cells expressing the inactive PTP1B have a spindle-shaped morphology, reduced adhesion and
spreading on fibronectin, and almost a complete absence of focal adhesions and stress fibers. Attachment
to fibronectin induces tyrosine phosphorylation of focal
adhesion kinase (FAK) and paxillin in parental cells
and cells transfected with the wild-type PTP1B, while in
cells transfected with the mutant PTP1B, such induction is not observed. Additionally, in cells expressing
the mutant PTP1B, tyrosine phosphorylation of Src is
enhanced and activity is reduced. Lysophosphatidic
acid temporarily reverses the effects of the mutant
PTP1B, suggesting the existence of a signaling pathway
triggering focal adhesion assembly that bypasses the
need for active PTP1B. PTP1B coimmunoprecipitates with
1-integrin from nonionic detergent extracts and
colocalizes with vinculin and the ends of actin stress fibers in focal adhesions. Our data suggest that PTP1B is
a critical regulatory component of integrin signaling
pathways, which is essential for adhesion, spreading,
and formation of focal adhesions.
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