Cell migration involves a multitude of signals that converge on cytoskeletal reorganization, essential for development, immune responses and tissue repair. Using knockdown and dominant negative approaches, we show that the microtubule-associated Ste20-like kinase SLK is required for focal adhesion turnover and cell migration downstream of the FAK/c-src complex. Our results show that SLK co-localizes with paxillin, Rac1 and the microtubules at the leading edge of migrating cells and is activated by scratch wounding. SLK activation is dependent on FAK/c-src/MAPK signaling, whereas SLK recruitment to the leading edge is src-dependent but FAK independent. Our results show that SLK represents a novel focal adhesion disassembly signal.

In the present study, we investigate the role of specific cytoplasmic tail (CT) regions of the D1A receptor in mediating dopamine (DA)-induced phosphorylation, desensitization and endocytosis. Results obtained in human embryonic kidney (HEK) cells expressing the wild-type (WT) or truncation forms (D425, D379 and D351) of the D1A receptor show that sequences located downstream of Gly379 regulate DA-mediated phosphorylation-dependent desensitization of D1A receptors. However, the longer truncation mutant D351 failed to undergo detectable DA-induced phosphorylation while exhibiting DA-induced desensitization features similar to the shorter truncation mutant D379. These data potentially suggest a novel role for a receptor phosphorylation-independent process in the DA-promoted D1A subtype desensitization. Our immunofluorescence data also suggest that sequences located between Cys351 and Gly379 play an important role in DA-mediated receptor endocytosis. Additionally, time-course studies were done in intact cells expressing WT or truncation receptors to measure the observed rate constant for adenylyl cyclase (AC) activation or k obs , a parameter linked to the receptor-G protein coupling status. In agreement with the desensitization data, D425-and D379-expressing cells exhibit an increase of k obs in comparison with WT-expressing cells. Nevertheless, D351-expressing cells, which harbor similar desensitization features of D379-expressing cells, display no change in k obs when compared with WT-expressing cells. Our results suggest that a defective DA-induced endocytosis may hamper D351 resensitization and concomitant increase in k obs . Thus, our study showing that specific D1A receptor CT sequences regulate DA-induced phosphorylation, desensitization, and endocytosis highlights the underlying molecular complexity of signaling at dopaminergic synapses.

We have previously shown that the Ste20-like kinase SLK is a microtubule-associated protein inducing actin stress fiber disassembly. Here, we show that v-Src expression can down-regulate SLK activity. This down-regulation is independent of focal adhesion kinase but requires v-Src kinase activity and membrane translocation. SLK down-regulation by v-Src is indirect and is accompanied by SLK hyperphosphorylation on serine residues. Deletion analysis revealed that casein kinase II (CK2) sites at position 347/348 are critical for v-Src-dependent modulation of SLK activity. Further studies show that CK2 can directly phosphorylate SLK at these positions and that inhibition of CK2 in v-Src-transformed cells results in normal kinase activity. Finally, CK2 and SLK can be co-localized in fibroblasts spreading on fibronectin-coated substrates, suggesting a mechanism whereby SLK may be regulated at sites of actin remodeling, such as membrane lamellipodia and ruffles, through CK2.Cell growth and differentiation are tightly regulated mechanisms involving a large number of signaling cascades. Dysregulation and accumulation of genetic aberrations in these signaling cascades are key components in the transformation of a normal cell to a cancer cell. Furthermore, a direct correlation has been found between the metastatic potential of cancers and the nature of the observed genetic mutations (1-5). Indeed, cellular transformation by the src oncogene, a non-receptor tyrosine kinase, results in loss of adherence, invasiveness, and metastasis through increased phosphorylation of adhesion proteins and cytoskeletal disorganization.c-Src and its viral counterpart v-Src are the most studied members of Src family kinases. Several studies have illustrated potential Src-mediated mechanisms regulating cell survival and apoptosis (6). In addition, studies have demonstrated altered c-Src kinase activity, and in some cases protein levels, in human cancers such as breast, colon, and pancreatic cancers (3). v-Src-transformed cells have been widely used to elicit the oncogenic effect of a constitutively active c-Src. Features characterizing these cancer cell line models include increased cell detachment and migration.Casein kinase II (CK2) 3 is a serine/threonine kinase tetramer complex composed of two catalytic subunits, ␣ and/or ␣Ј and/or ␣Љ and two regulatory ␤ subunits. CK2 minimal amino acid consensus phosphorylation sequence is Ser-X-X-acidic, where the acidic residue can be glutamic acid, aspartic acid, phospho-Ser, or phospho-Tyr (7). CK2 is referred to as "a housekeeping enzyme," given its increasing number of substrates (Ͼ300). A role for CK2 has been shown in a wide range of cellular functions and properties such as cell proliferation, survival, differentiation, transformation, and tumorigenesis (8 -12). Recently, the CK2␣ subunit has been shown to be phosphorylated by the Src family kinases, c-Fgr and c-Lyn, resulting in increased catalytic activity (13).Previous studies in our laboratory have shown that the Ste20-like kinase SLK is redi...

Urodele amphibians, such as the newt Notophthalmus viridescens, have the unique ability to regenerate limbs, spinal cord, eye structures, and many vital organs through a process called epimorphic regeneration. Although the cellular basis of regeneration has been studied in detail, we know relatively little about the molecular controls of the process. This review provides an overview of forelimb regeneration in the newt, addressing what we know about cellular and molecular aspects. Particular focus is placed on the dedifferentiation process, which yields a population of embryonic-like pluripotent cells that will eventually reform the lost structure. This cellular plasticity seems to be the key to regenerative ability. We discuss the dedifferentiation process in newt forelimb regeneration and outline the various studies that have revealed that mammalian cells also have the ability to dedifferentiate if given the appropriate triggers.

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