Comparative genomics on HHIP family orthologs

Abstract

Hedgehog, FGF, VEGF, and Notch signaling pathways network together for vascular remodeling during embryogenesis and carcinogenesis. HHIP1 (HHIP) is an endogenous antagonist for SHH, IHH, and DHH. Here, comparative integromics analyses on HHIP family members were performed by using bioinformatics and human intelligence. HHIP1, HHIP2 (HHIPL1 or KIAA1822) and HHIP3 (HHIPL2 or KIAA1822L) constitute human HHIP gene family. Rat Hhip1, Hhip2, and Hhip3 genes were identified within AC107504.4, AC094820.6, and AC134264.2 genome sequences, respectively. HHIP-homologous (HIPH) domain with conserved 18 Cys residues was identified as the novel domain conserved among mammalian HHIP1, HHIP2, and HHIP3 orthologs. HHIP1 mRNA was expressed in coronary artery endothelial cells, prostate, and rhabdomyosarcoma. HHIP2 mRNA was expressed in trabecular bone cells. HHIP3 mRNA was expressed in testis, thyroid gland, osteoarthritic cartilarge, pancreatic cancer, and lung cancer. Promoters of HHIP family genes were not well conserved between human and rodents. Although GLI-, CSL-, and HES/HEY-binding sites were not identified, eleven bHLH-binding sites were identified within human HHIP1 promoter. Expression of HES/HEY family members, including HES1, HES2, HES3, HES4, HES5, HES6, HES7, HEY1, HEY2 and HEYL, in coronary artery endothelial cells was not detected in silico. Up-regulation of HHIP1 due to down-regulation of Notch-CSL-HES/HEY signaling cascade repressing bHLH transcription factors results in down-regulation of the Hedgehog-VEGF-Notch signaling cascade. On the other hand, down-regulation of HHIP1 due to up-regulation of Notch signaling in vascular endothelial cells during angiogenesis results in up-regulation of the Hedgehog-VEGF-Notch signaling cascade. Because HHIP1 is the key molecule for vascular remodeling, HHIP1 is the pharmacogenomics target in the fields of oncology and vascular medicine.