Skelemin in integrin α(IIb)β(3) mediated cell spreading

Integrin α(IIb)β(3) plays a central role in cell adhesion and spreading. Prior research has shown that integrin clustering activates signaling pathways involving focal adhesion kinase and Src. However, the role of skelemin, a myosin-associated protein, in integrin signaling remains unclear. No prior work had resolved how skelemin influences integrin clustering or cytoskeletal organization during early spreading. This gap motivated the investigation of skelemin's role in integrin-mediated cell spreading. Existing knowledge suggested that integrin signaling involves multiple cytoskeletal proteins. Yet, the specific contribution of skelemin to this process was unknown. This study aimed to clarify whether skelemin modulates integrin signaling and cytoskeletal reorganization. Understanding these mechanisms could provide new insights into cell adhesion dynamics.

The study aimed to determine how skelemin influences integrin α(IIb)β(3) signaling and cytoskeletal organization during early cell spreading. Researchers focused on the interaction between skelemin and integrin residues in the membrane proximal region. They hypothesized that specific residues affect cell adhesion and spreading. The goal was to assess whether skelemin binding modulates integrin clustering and signaling. The study also sought to identify which integrin residues are critical for skelemin interaction. Researchers examined the effects of skelemin on focal adhesion formation and stress fiber organization. They tested whether skelemin binding influences Src activation in spreading cells. The findings could clarify how integrin signaling is regulated during cell adhesion.

Researchers generated Chinese hamster ovary cells expressing wild-type or mutant α(IIb)β(3) integrin receptors. Specific residues in the integrin tail were mutated to alanine to disrupt skelemin binding. Cell adhesion and spreading were assessed on immobilized fibrinogen substrates. Focal adhesion and stress fiber formation were analyzed using fluorescent labeling. Cells were transfected with GFP-skelemin containing only the integrin-binding domain. Spreading behavior was compared between wild-type and mutant integrin-expressing cells. Src and focal adhesion kinase activation were measured using phospho-specific antibodies. Colocalization of talin and integrin was examined in mutant cells to assess binding loss.

Most mutant cells showed normal adhesion and spreading on fibrinogen substrates. R995A/R997A/L1000A, H722A, and K716A mutants exhibited enhanced spreading and p-Src activation. These mutants showed no signs of impaired focal adhesion or stress fiber formation. Transfection with C2 domain of skelemin caused wild-type cells to round up. However, this had no effect on R995A/R997A/L1000A, H722A, and K716A mutant cells. K716A cells showed strong talin colocalization with α(IIb)β(3) integrin at the leading edge. This colocalization was associated with a loss of skelemin binding in mutant cells. These findings suggest that skelemin modulates integrin clustering and Src activation during spreading.

The authors propose that skelemin exerts contractile force during early cell spreading. Skelemin binding modulates integrin clustering and cytoskeletal protein attachment. Enhanced spreading in specific mutants correlates with increased p-Src activation. These findings suggest that skelemin influences Src signaling in spreading cells. The loss of skelemin binding in K716A mutants correlates with talin colocalization. This supports a role for skelemin in regulating integrin-mediated signaling. The study does not claim that skelemin is essential for spreading but suggests it modulates it. The results align with the hypothesis that skelemin regulates cytoskeletal organization.