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Karen H Martin

Publications and source records attributed to Karen H Martin.

6 recordsLinked to original sources
PubMed2005

Focal adhesion kinase is required for the spatial organization of the leading edge in migrating cells.

The process of cell migration is initiated by protrusion at the leading edge of the cell, the formation of peripheral adhesions, the exertion of force on these adhesions, and finally the release of the adhesions at the rear of the cell. Focal adhesion kinase (FAK) is intimately involved in the regulation of this process, although the precise mechanism(s) whereby FAK regulates cell migration is unclear. We have used two approaches to reduce FAK expression in fibroblasts. Treatment of cells with FAK-specific siRNAs substantially reduced FAK expression and inhibited the spreading of fibroblasts in serum-free conditions, but did not affect the rate of spreading in the presence of serum. In contrast with the wild-type cells, the FAK siRNA-treated cells exhibited multiple extensions during cell spreading. The extensions appeared to be inappropriately formed lamellipodia as evidenced by the localization of cortactin to lamellipodial structures and the inhibition of such structures by expression of dominant-negative Rac. The wild-type phenotype was restored by reexpressing wild-type FAK in the knockdown cells, but not by expression of FAK containing a point mutation at the autophosphorylation site (FAK Y397F). In wound-healing assays, FAK knockdown cells failed to form broad lamellipodia, instead forming multiple leading edges. Similar results were obtained using primary mouse embryo fibroblasts from FAK-flox mice in which Cre-mediated excision was used to ablate the expression of FAK. These data are consistent with a role for FAK in regulating the formation of a leading edge during cell migration by coordinating integrin signaling to direct the correct spatial activation of membrane protrusion.

Animals↗
PubMed2002

Integrin connections map: to infinity and beyond.

Integrins are transmembrane proteins that serve as primary sensors of the extracellular matrix (ECM) environment. In response to interactions with the ECM, integrins initiate signaling pathways that regulate cell migration, growth, and survival. Advances in imaging have contributed to the understanding of the dynamic nature of these cell-ECM interactions and the complexes that form at these sites and have provided insights into their regulation and signal organizing functions.

Actin Cytoskeleton↗
PubMed2002

Regulation of focal adhesion targeting and inhibitory functions of the FAK related protein FRNK using a novel estrogen receptor "switch".

Focal adhesion kinase (FAK) is a regulator of numerous adhesion-dependent processes including cell migration, cell proliferation, and cell survival. The C-terminal domain of FAK, FAK-related nonkinase (FRNK), is autonomously expressed and functions as an inhibitor of FAK signaling. Previous attempts to use FRNK as a tool to dissect FAK signaling have been limited because of an inability to temporally regulate the inhibitory functions of FRNK. In this report, we describe and characterize a conditionally targeted form of FRNK that was created by fusing the hormone-binding domain of the estrogen receptor (ER*) to the C-terminus of FRNK. In the absence of added hormone, FRNK-ER* was diffusely distributed throughout the cytoplasm of cells. Upon addition of hormone, the cytoplasmic pool of FRNK-ER* was rapidly redistributed to focal adhesions. We demonstrate that cells expressing FRNK-ER* show a hormone-dependent decrease in FAK tyrosine phosphorylation and cell migration. Furthermore, when cells expressing of FRNK-ER* were treated with hormone, the cells responded with a dramatic change in cell morphology, suggesting a role for FAK in the regulation of the adhesive properties of focal adhesions.

Animals↗
PubMed2002

The association of ASAP1, an ADP ribosylation factor-GTPase activating protein, with focal adhesion kinase contributes to the process of focal adhesion assembly.

ASAP1 (ADP ribosylation factor [ARF]- GTPase-activating protein [GAP] containing SH3, ANK repeats, and PH domain) is a phospholipid-dependent ARF-GAP that binds to and is phosphorylated by pp60(Src). Using affinity chromatography and yeast two-hybrid interaction screens, we identified ASAP1 as a major binding partner of protein tyrosine kinase focal adhesion kinase (FAK). Glutathione S-transferase pull-down and coimmunoprecipitation assays showed the binding of ASAP1 to FAK is mediated by an interaction between the C-terminal SH3 domain of ASAP1 with the second proline-rich motif in the C-terminal region of FAK. Transient overexpression of wild-type ASAP1 significantly retarded the spreading of REF52 cells plated on fibronectin. In contrast, overexpression of a truncated variant of ASAP1 that failed to bind FAK or a catalytically inactive variant of ASAP1 lacking GAP activity resulted in a less pronounced inhibition of cell spreading. Transient overexpression of wild-type ASAP1 prevented the efficient organization of paxillin and FAK in focal adhesions during cell spreading, while failing to significantly alter vinculin localization and organization. We conclude from these studies that modulation of ARF activity by ASAP1 is important for the regulation of focal adhesion assembly and/or organization by influencing the mechanisms responsible for the recruitment and organization of selected focal adhesion proteins such as paxillin and FAK.

Animals↗