LIM kinases (LIMK1 and LIMK2) are LIM domain containing
serine/threonine kinases that modulate reorganization of actin cytoskeleton through inactivating phosphorylation of
cofilin. The Rho family of
small GTPases regulates the catalytic activity of LIMK1 and LIMK2 through activating phosphorylation by ROCK or by p21
kinase. Recent studies have suggested that LIMK1 could play a role in modulation of cellular growth by alteration of the cell cycle in breast and prostate
tumor cells; however, the direct mitogenic effects of LIMK1 in these
tumor cells is yet to be elucidated. Via immunofluorescence, in this study, we show that phosphorylated
LIM kinases (pLIMK1/2) are colocalized with
gamma-tubulin in the centrosomes during the early mitotic phases of human breast and
prostate cancer cells (MDA-MB-231 and DU145); apparent colocalization begins in the centrosomes in prophase. As shown by both bright field (MDA-MB-231) and fluorescent immunohistochemistry (MDA-MB-231 and DU145), pLIMK1/2 does not localize to centrosomes during interphase. By bright field immunohistochemistry, the largest area of the centrosome that is stained with pLIMK1/2 occurs at anaphase. In early telophase, reduced staining of pLIMK1/2 at the spindle poles and concomitant accumulation of pLIMK1/2 at the cleavage furrow begins to occur. In late telophase, loss of staining of pLIMK1/2 and of colocalization with
gamma-tubulin occurs at the poles and pLIMK1/2 became further concentrated at the junction between the two daughter cells. Co-immunoprecipitation studies indicated that
gamma-tubulin associates with phosphorylated LIMK1 and LIMK2 but not with dephosphorylated LIMK1 or LIMK2. The results suggest that activated LIMK1/2 may associate with
gamma-tubulin and play a role in mitotic spindle assembly.