Sine oculis homeobox homolog 1 (SIX1)

Sine oculis homeobox homolog 1 (SIX1) is a highly conserved homeodomain-containing transcription factor that belongs to the SIX gene family[1]. The protein is characterized by a divergent DNA-binding homeodomain and an upstream SIX domain, which determines DNA-binding specificity and mediates protein-protein interactions[1]. SIX1 plays a pivotal role during embryogenesis by regulating organogenesis, particularly in the development of muscles, kidneys, ears, and craniofacial structures[5]. The protein functions primarily through interaction with Eyes Absent (EYA) co-activators, forming transcriptional complexes essential for driving developmental programs[2][5]. In normal development, SIX1 regulates the expression of various proteins involved in organ development, including its role in skeletal muscle fiber-type specification and nephron progenitor cell regulation[7]. However, aberrant expression of SIX1 has significant pathological implications. Mutations in the SIX1 gene cause branchio-oto-renal (BOR) and branchio-otic (BO) syndromes, which are characterized by hearing impairment, renal anomalies, and branchial arch defects[2][4]. In cancer contexts, SIX1 acts as a potent oncogene when inappropriately reactivated in adult tissues, contributing to malignant transformation by transcriptionally upregulating cell cycle regulators such as cyclin A1 and cyclin D1, thereby promoting cell proliferation in various cancers including breast and pancreatic carcinoma[3][5]. The protein's transcriptional activity is modulated through post-translational modifications including phosphorylation and ubiquitination, and its function is critically dependent on proper protein-protein interactions and DNA-binding capacity[2][3].

Other names

Homeobox protein SIX1SIX homeobox 1BOS3DFNA23TIP39sine oculis homeobox homolog 1

Transcriptional activation, DNA binding, Protein-protein interaction with cofactors