Homeodomain-only protein （HOPX） functions via its interaction with SRF， thus modulating the expression of SRF-dependent cardiac-specific genes and cardiac development. HOPX inhibits SRF-dependent transcription either by hindering SRF binding to DNA or by engaging histone deacetylase （HDAC） proteins which prevent transcription by SRF. HOPX is a homeodomain protein which lacks certain conserved residues required for DNA binding. HOPX overexpression causes cardiac hypertrophy.
