Galectin-3: A novel substrate for c-Abl kinase.

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• Galectin-3 is a beta-galactoside-binding lectin with diverse cellular functions, including roles in cell growth, adhesion, and interaction.
• Its biological activity, particularly its pro- or anti-apoptotic effects, is influenced by cellular localization and post-translational modifications like cleavage and phosphorylation.
• Phosphorylation of galectin-3 is known to modulate its sugar-binding capabilities.

Purpose of the Study:

• To identify novel tyrosine phosphorylation sites on galectin-3.
• To determine the specific kinase responsible for phosphorylating these sites.
• To investigate the functional consequences of galectin-3 phosphorylation at identified sites.

Main Methods:

• In vitro and in vivo phosphorylation assays were performed to identify and confirm tyrosine phosphorylation sites on galectin-3.
• Mass spectrometry was utilized to pinpoint specific tyrosine residues targeted for phosphorylation.
• The kinase activity of c-Abl was assessed in relation to galectin-3 phosphorylation.
• Galectin-3 null SK-Br-3 cells were used to express wild-type and mutant galectin-3 (Y107F) for functional studies.

Main Results:

• Novel tyrosine phosphorylation sites were identified at positions 79, 107, and 118 of galectin-3.
• The c-Abl kinase was identified as the responsible kinase for phosphorylating these tyrosine residues.
• Tyrosine 107 was determined to be the primary phosphorylation target of c-Abl on galectin-3.
• Expression of a galectin-3 Y107F mutant in galectin-3 null cells resulted in altered cell morphology and increased motility compared to cells expressing wild-type galectin-3.

Conclusions:

• The study identified c-Abl as a novel kinase that phosphorylates galectin-3 at specific tyrosine residues (79, 107, 118), with Tyr107 being a major site.
• Phosphorylation of galectin-3, particularly at Tyr107, influences cellular morphology and motility.
• Further research is warranted to fully elucidate the functional significance of these novel phosphorylation events in galectin-3 biology.