Phosphorylation on Ser106 modulates the cellular functions of the SHOX homeodomain protein

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Mutations in the SHOX gene are linked to skeletal disorders like Léri-Weill syndrome, indicating its role in growth.
• The precise function of SHOX and its regulatory mechanisms are not fully understood.
• Previous research identified SHOX as a nuclear transcriptional activator that can induce cell-cycle arrest and apoptosis.

Purpose of the Study:

• To investigate if SHOX protein is a target for phosphorylation.
• To identify the specific phosphorylation sites and the kinases involved.
• To determine the functional significance of SHOX phosphorylation.

Main Methods:

• In vivo and in vitro phosphorylation analysis of SHOX.
• Two-dimensional phospho-peptide mapping to identify phosphorylation sites.
• Site-directed mutagenesis to create non-phosphorylatable SHOX mutants (S106A).
• In vitro kinase assays using casein kinase II (CKII).
• Assessment of transcriptional activity and cellular effects (cell-cycle arrest, apoptosis) of wild-type and mutant SHOX.

Main Results:

• SHOX is phosphorylated on serine residues in vivo.
• Serine 106 was identified as the major phosphorylation site.
• Casein kinase II efficiently phosphorylates SHOX on serine 106 in vitro.
• CKII inhibitors reduced SHOX phosphorylation in vivo.
• A serine 106 mutant (S106A) showed impaired transcriptional activation, cell-cycle arrest, and apoptosis induction.

Conclusions:

• SHOX phosphorylation, particularly at serine 106 by casein kinase II, is a key regulatory mechanism.
• Phosphorylation of SHOX is essential for its biological activities, including transcriptional activation and induction of cell-cycle arrest and apoptosis.
• Understanding SHOX phosphorylation provides insights into skeletal development and related disorders.