Multifunctional Role of the Pitx2 Homeodomain Protein C-Terminal Tail

Abstract

Pitx2 is a newly described bicoid-like homeodomain transcription factor that is defective in Rieger syndrome and shows a striking leftward developmental asymmetry. We have previously shown that Pitx2 (also called Ptx2 and RIEG) transactivates a reporter gene containing a bicoid enhancer and synergistically transactivates the prolactin promoter in the presence of the POU homeodomain protein Pit-1. In this report, we focused on the C-terminal region which is mutated in some Rieger patients and contains a highly conserved 14-amino-acid element. Deletion analysis of Pitx2 revealed that the C-terminal 39-amino-acid tail represses DNA binding activity and is required for Pitx2-Pit-1 interaction and Pit-1 synergism. Pit-1 interaction with the Pitx2 C terminus masks the inhibitory effect and promotes increased DNA binding activity. Interestingly, cotransfection of an expression vector encoding the C-terminal 39 amino acids of Pitx2 specifically inhibits Pitx2 transactivation activity. In contrast, the C-terminal 39-amino-acid peptide interacts with Pitx2 to increase its DNA binding activity. These data suggest that the C-terminal tail intrinsically inhibits the Pitx2 protein and that this inhibition can be overcome by interaction with other transcription factors to allow activation during development.

At least two expressed genes for transcription factors Pitx2 and Rpx are present in common carp and are upregulated during winter acclimatization

“…No substitution occurred in the homeo-domain or in the C-terminal OAR 254 domain, only minor differences are found in the central part of the sequence 255 (Furukata et al, 1997). These observations confirm the importance of these two 256 conserved regions, which are involved in DNA-binding and/or interaction with other 257 transcriptional cofactors (Olson et al, 2003;Amendt et al, 1998Amendt et al, , 1999. One 258 interesting feature is the doublet substitution SA in cPitx2-I to PT in cPitx2-II, 259 compared to the zebrafish PA sequence at position 1013 (Fig.…”

“…Different 79 mutations affecting human PITX2 DNA-binding or trans-activation have been 80 described in Rieger patients (Quentien et al, 2006). Besides its N-terminal, 81 conserved DNA binding homeodomain, the Pitx2 factor contains a C-terminal domain 82 (OAR, otp-, aristaless-, rax-domain) that is involved in regulation of DNA-binding and 83 transcriptional activation (Amendt et al, 1999). 84 Rpx1 (Hesx1, Anf1) is a transcriptional repressor transiently expressed in the mouse 85 pituitary primordium and playing a role in early determination and differentiation 86 (Hermesz et al, 2003).…”

The Identification of Prx1 Transcription Regulatory Domains Provides a Mechanism for Unequal Compensation by thePrx1 and Prx2 Loci

“…Carboxyl inhibitory or masking domains are common regulatory motifs observed in a number of transcription factors including PHO4, c-Myb, Pax2, Pax5, Pax8, C/EBP␤(NF-M), Nkx2.5, and Pitx2 (11,(41)(42)(43)(44)(45). The mechanism of action for these inhibitory domains varies depending on the transcription factor examined.…”

“…1). Predominance of these residues is associated with transcription regulatory regions in other proteins (6,11,(22)(23)(24)(25)(26).…”

“…The function of the OAR domain is not well understood; however, three proteins with an OAR domain have been examined. In the Prx2 and Pitx2 homeoproteins, the OAR domain has been defined as inhibiting transactivation (6,11). For the Otp homeoprotein, the OAR domain may either be a transactivator or have an adjacent transactivation domain (12).…”