Complex Csf3r Protein Isoform Interactions Dictate Cytokine Responsiveness

CSF3R, the receptors for granulocyte colony stimulating factor, is a critical regulator of neutrophil production. Multiple CSF3R mRNA transcripts have been identified and are annotated in Genbank. The expression and function of the different CSF3R proteins have not been fully elucidated. We generated antibodies specific for two of the identified and annotated isoforms, V3 and V4. CSF3R-V4 is a truncated variant of V1 with a unique C-terminal 34 amino acids and this variant confers enhanced growth signals. Changes in the ratio of V1:V4 isoforms have been implicated in chemotherapy resistance and relapse of AML. CSF3R-V3 is a variant of V1 with a 27 amino acid insertion between two conserved domains in the cytoplasmic portion of the receptor involved in JAK/STAT activation, termed the box 1 and box 2. CSF3R-V3 produces reduced proliferative signaling in response to G-CSF. When V3 is co-expressed with V1, proliferative signaling is reduced in a concentration dependent manner.