Involved in EGFR trafficking, acting as negative regulator of endocytic EGFR internalization at the plasma membrane. Monomer (By similarity). Can also form homodimers (By similarity). Interacts with TARDBP; the interaction is RNA-dependent (PubMed:20740007). Interacts with RBFOX1 (PubMed:10814712). Interacts with polyribosomes (PubMed:16835262). Interacts with SH3GL2 and SH3GL3 (PubMed:18602463). Interacts with SH3KBP1 and CBL (By similarity). Interacts with EGFR (PubMed:18602463). Interacts with ATXN2L (PubMed:23209657). Expressed in the brain, heart, liver, skeletal muscle, pancreas and placenta. Isoform 1 is predominant in the brain and spinal cord. Isoform 4 is more abundant in the cerebellum. In the brain, broadly expressed in the amygdala, caudate nucleus, corpus callosum, hippocampus, hypothalamus, substantia nigra, subthalamic nucleus and thalamus. The poly-Gln region of ATXN2 is polymorphic: 17 to 29 repeats are found in the normal population. Higher numbers of repeats result in different disease phenotypes depending on the length of the expansion. The disease is caused by variants affecting the gene represented in this entry. SCA2 is caused by expansion of a CAG repeat resulting in about 36 to 52 repeats in some patients. Longer expansions result in earlier the expansion, onset of the disease. Disease susceptibility is associated with variants affecting the gene represented in this entry. An increased risk for developing amyotrophic lateral sclerosis seems to be conferred by CAG repeat intermediate expansions greater than 23 but below the threshold for developing spinocerebellar ataxia. Belongs to the ataxin-2 family.