Human Cart-1: Structural Organization, Chromosomal Localization, and Functional Analysis of a Cartilage-Specific Homeodomain cDNA

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Abstract
Homeoproteins control cell fates during development, specifying pattern formation and the ontogeny of specific tissues and organs in embryogenesis. Cart-1 cDNA was recently cloned from a rat chondrosarcoma tumor and it encodes a protein containing a paired-like homeodomain that is selectively expressed in cartilage during early chondrocyte differentiation. Here we report the molecular cloning of the human Cart-1 cDNA from a HeLa cervical carcinoma cDNA library. The human Cart-1 cDNA sequence is 88% identical and the deduced amino acid sequence is 95% identical to the rat sequence, indicating that Cart-1 structure is highly conserved. Northern and reverse transcriptase polymerase chain reaction (RT-PCR) analysis revealed Cart-1 mRNA expression in HeLa cervical carcinoma cells and human cervical tissue, but Cart-1 mRNA was not detected in GH3 rat pituitary cells and murine 10T½ one-half fibroblast cells. The Cart-1 gene was localized to human chromosome 12 and regionally mapped to the 12q21.3–q22 by PCR analysis of rodent-x-human somatic cell hybrid DNA and the CEPH megabase-insert YAC DNA pools, respectively. The Holt-Oram syndrome, characterized by upper limb and atrial septal dysplasias, also maps to the 12q21.3–q22 region. Cotransfection studies show that Cart-1 inhibits the rat prolactin promoter and that this repression is mediated by footprint II, an AT-rich element that functions as an inhibitory site of prolactin gene expression in nonpituitary cells and which was used to clone Cart-1. Taken together, these data indicate that Cart-1 may also influence cervix development, identify a putative DNA binding site for Cart-1, and, begin to define its functional role as modulator of gene expression.