The Tyrosine Kinase Activity of c-Src Regulates Actin Dynamics and Organization of Podosomes in Osteoclasts

Podosomes are dynamic actin-rich structures composed of a dense F-actin core surrounded by a cloud of more diffuse F-actin. Src performs one or more unique functions in osteoclasts (OCLs), and podosome belts and bone resorption are impaired in the absence of Src. Using Src−/−OCLs, we investigated the specific functions of Src in the organization and dynamics of podosomes. We found that podosome number and the podosome-associated actin cloud were decreased in Src−/−OCLs. Videomicroscopy and fluorescence recovery after photobleaching analysis revealed that the life span of Src−/−podosomes was increased fourfold and that the rate of actin flux in the core was decreased by 40%. Thus, Src regulates the formation, structure, life span, and rate of actin polymerization in podosomes and in the actin cloud. Rescue of Src−/−OCLs with Src mutants showed that both the kinase activity and either the SH2 or the SH3 binding domain are required for Src to restore normal podosome organization and dynamics. Moreover, inhibition of Src family kinase activities in Src−/−OCLs by Src inhibitors or by expressing dominant-negative SrcK295Minduced the formation of abnormal podosomes. Thus, Src is an essential regulator of podosome structure, dynamics and organization.

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ACK Family Tyrosine Kinase Activity Is a Component of Dcdc42 Signaling during Dorsal Closure in Drosophila melanogaster

Molecular and Cellular Biology ◽

10.1128/mcb.22.11.3685-3697.2002 ◽

2002 ◽

Vol 22 (11) ◽

pp. 3685-3697 ◽

Cited By ~ 15

Author(s):

Kai Ping Sem ◽

Baharak Zahedi ◽

Ivan Tan ◽

Maria Deak ◽

Louis Lim ◽

...

Keyword(s):

Drosophila Melanogaster ◽

Tyrosine Kinase ◽

Kinase Activity ◽

Leading Edge ◽

Small Gtpase ◽

Dominant Negative ◽

Binding Motif ◽

Dorsal Closure ◽

Tyrosine Kinase Activity ◽

Amino Terminal

ABSTRACT We have characterized Drosophila melanogaster ACK (DACK), one of two members of the ACK family of nonreceptor tyrosine kinases in Drosophila. The ACKs are likely effectors for the small GTPase Cdc42, but signaling by these proteins remains poorly defined. ACK family tyrosine kinase activity functions downstream of Drosophila Cdc42 during dorsal closure of the embryo, as overexpression of DACK can rescue the dorsal closure defects caused by dominant-negative Dcdc42. Similar to known participants in dorsal closure, DACK is enriched in the leading edge cells of the advancing epidermis, but it does not signal through activation of the Jun amino-terminal kinase cascade operating in these cells. Transcription of DACK is responsive to changes in Dcdc42 signaling specifically at the leading edge and in the amnioserosa, two tissues involved in dorsal closure. Unlike other members of the ACK family, DACK does not contain a conserved Cdc42-binding motif, and transcriptional regulation may be one route by which Dcdc42 can affect DACK function. Expression of wild-type and kinase-dead DACK transgenes in embryos, and in the developing wing and eye, reveals that ACK family tyrosine kinase activity is involved in a range of developmental events similar to that of Dcdc42.

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Morphological Differentiation of Oligodendrocytes Requires Activation of Fyn Tyrosine Kinase

The Journal of Cell Biology ◽

10.1083/jcb.145.6.1209 ◽

1999 ◽

Vol 145 (6) ◽

pp. 1209-1218 ◽

Cited By ~ 149

Author(s):

Donna J. Osterhout ◽

Amy Wolven ◽

Rebecca M. Wolf ◽

Marilyn D. Resh ◽

Moses V. Chao

Keyword(s):

Tyrosine Kinase ◽

Kinase Activity ◽

Kinase Inhibitors ◽

Morphological Differentiation ◽

Dominant Negative ◽

Tyrosine Kinase Activity ◽

Oligodendrocyte Progenitors ◽

Differentiated Cells ◽

Process Formation ◽

Fyn Tyrosine Kinase

In the central nervous system, myelination of axons occurs when oligodendrocyte progenitors undergo terminal differentiation and initiate process formation and axonal ensheathment. Although it is hypothesized that neuron-oligodendrocyte contact initiates this process, the molecular signals are not known. Here we find that Fyn tyrosine kinase activity is upregulated very early during oligodendrocyte progenitor cell differentiation. Concomitant with this increase is the appearance of several tyrosine phosphorylated proteins present only in differentiated cells. The increased tyrosine kinase activity is specific to Fyn, as other Src family members are not active in oligodendrocytes. To investigate the function of Fyn activation on differentiation, we used Src family tyrosine kinase inhibitors, PP1 and PP2, in cultures of differentiating oligodendrocyte progenitors. Treatment of progenitors with these compounds prevented activation of Fyn and reduced process extension and myelin membrane formation. This inhibition was reversible and not observed with related inactive analogues. A similar effect was observed when a dominant negative Fyn was introduced in progenitor cells. These findings strongly suggest that activation of Fyn is an essential signaling component for the morphological differentiation of oligodendrocytes.

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