Divergent pathways in COS-7 cells mediate defective internalization and intracellular routing of truncated G-CSFR...

Area of Science:

• Cell biology
• Molecular biology
• Hematology

Background:

• Truncated G-CSFR forms in Severe Congenital Neutropenia (SCN) and Acute Myeloid Leukemia (AML) patients cause hyperproliferation and prolonged cell survival.
• Previous studies indicated delayed ligand internalization and defective degradation of truncated G-CSFR in SCN/AML patients.

Purpose of the Study:

• To investigate the roles of dileucine and tyrosine-based motifs in the G-CSFR cytoplasmic domain on ligand/receptor internalization.
• To determine if G-CSFR internalization and degradation are independent processes.

Main Methods:

• Standard binding assays with radiolabeled ligand and COS-7 cells.
• Investigated substitutions in dileucine motifs and deletions of tyrosine residues in G-CSFR.
• Assessed the effect of attaching the transferrin receptor YTRF internalization motif to a truncated G-CSFR form.

Main Results:

• G-CSFR internalization was not altered by substitutions in the dileucine motif or deletion of tyrosine residues.
• Attaching the transferrin receptor YTRF internalization motif corrected defective internalization of a truncated G-CSFR form from an SCN/AML patient.
• Receptor degradation was not corrected by the YTRF motif, suggesting independent mechanisms for internalization and degradation.

Conclusions:

• Distinct domains within the G-CSFR mediate separate processes for receptor internalization and degradation.
• Findings from standard binding assays differ from recent flow cytometry data.