Hox Proteins Functionally Cooperate with the GC Box-binding Protein System through Distinct Domains

Abstract

Hox genes encode a transcriptional factor that plays a key role in regulating position-specific cartilage pattern formation. We found that Hoxa-13 and Hoxd-13, which are members of the Abd-B subfamily of Hox genes and are crucial for the autopod development of the limb, stimulate transcription from the Bmp-4 promoter. This stimulation was dependent on the GC box within the promoter and independent of the putative Hox protein binding site. The stimulation by HoxA-13 was remarkably enhanced by cotransfection with members of a family of zinc finger GC box binding transcriptional factors including Sp1. The stimulation was suppressed by another Abd-B Hox protein, HoxA-11, indicating that each Abd-B Hox protein has a different effect on the target genes through the Sp1 system. We have identified multiple functional domains involved in transcriptional regulation, including three independent transcriptional activation domains (ADs) in HoxA-13. AD1 and AD3 in helices 1 and 2 of the homeodomain individually cooperate with Sp1-dependent stimulation. The homeodomain is also required for cooperation of the AD with Sp1. By contrast, AD2 strongly activates transcription in an Sp1-independent manner only when the homeodomain has been removed. These observations indicate that HoxA-13 regulates transcription through multiple pathways. In addition, we found that a helix 3 mutation of the HoxA-13 homeodomain behaves as a dominant negative form.

HOXA13 regulates the expression of bone morphogenetic proteins 2 and 7 to control distal limb morphogenesis

“…Previous investigations of HOXA13 function indicate that Bmp4 expression may also be regulated by HOXA13 DNAbinding (Suzuki et al, 2003). However, by our analysis, the expression of Bmp4 appears to be normal in Hoxa13 mutant limbs (data not shown), suggesting that the cooperative regulation of Bmp4 by SP1 may compensate for the loss of HOXA13 DNA-binding function.…”

The RHOX5 Homeodomain Protein Mediates Transcriptional Repression of the Netrin-1 Receptor Gene Unc5c

“…However, there have been instances of homeobox transcription factors acting independently of their homeodomain by "piggy-backing" on other transcription factors (44). To determine whether its homeodomain is required for RHOX5 to repress Unc5c expression, we constructed a mutant Rhox5 expression plasmid encoding a truncated RHOX5 protein that has the intact N-terminal part and C-terminal part of RHOX5 but lacks the entire homeodomain (HD) (Fig.…”

Molecular genetic cascades for external genitalia formation: An emerging organogenesis program

“…Compound Hoxa-13 and Hoxd-13 null mice have defects in the anal sphincter and the absence of an anal opening (Warot et al, 1997). Although it is becoming clear that the Hox genes play an important role in the development of the lower gastrointestinal, urogenital/reproductive system and the GT, further molecular and genetic studies are necessary to elucidate the genetic cascade in relation to other regulatory genes or their downstream genes (Stadler et al, 2001, Morgan et al, 2003Suzuki et al, 2003b;Knosp et al, 2004;Yin and Ma, 2005). Searching for the Hox downstream genes utilizing target chromosome isolation is in progress (Morgan et al, 2003).…”

“…Searching for the Hox downstream genes utilizing target chromosome isolation is in progress (Morgan et al, 2003). These strategies include Hox interaction partner assays during limb formation (Suzuki et al, 2003b;Knosp et al, 2004;Chen et al, 2004).…”