Target-dependent Effect of Phosphorylation on the DNA Binding Activity of the TAL1/SCL Oncoprotein

doi:10.1074/jbc.272.17.11457

Target-dependent Effect of Phosphorylation on the DNA Binding Activity of the TAL1/SCL Oncoprotein*

From the Departments of ^‡ Medicine and
^§ Cell Biology, Vanderbilt University Medical Center and the
^¶ Department of Veterans Affairs Medical Center, Nashville, Tennessee 37232

^∥ To whom correspondence should be addressed:
Division of Hematology, Rm. 547 MRB II, Vanderbilt University Medical Center, Nashville, TN 37232.
Tel.: 615-936-1809; Fax: 615-936-1812.

Abstract

Activation of the TAL1 (or SCL) gene, initially identified through its involvement by a recurrent chromosomal translocation, is the most frequent gain-of-function mutation recognized in T-cell acute lymphoblastic leukemia. The translational products of this gene contain the basic domain helix-loop-helix motif characteristic of a family of transcription factors that bind to a consensus nucleotide sequence termed the E-box. Previous work established that the TAL1 proteins are phosphorylated exclusively on serine and identified Ser¹²² as a substrate for the mitogen-activated protein kinase ERK-1. We provide evidence that an additional serine residue, Ser¹⁷², located in a conserved region proximal to the DNA binding domain and sharing homology with a similarly positioned sequence in the HLH oncoprotein LYL1, can be phosphorylated in vitro and in vivo by the catalytic subunit of cAMP-dependent protein kinase. Phosphorylation was found to alter TAL1 DNA binding activity in a target-dependent manner that was influenced by both the specific CANNTG E-box core motif and its flanking sequences. In contrast, the ability of TAL1 to interact with the E2A gene product E12 and its subcellular localization in transfected COS cells were unaffected by Ser¹⁷² phosphorylation. These results suggest this serine residue has a regulatory function and indicate a mechanism by which phosphorylation could affect DNA binding site discrimination.

Footnotes

↵* This work was supported in part by United States Public Health Service Grant R29 HL49118 (to S. J. B.) and by the Lucille P. Markey Charitable Trust (to S. J. B.). The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹ The abbreviations used are:

HLH

helix-loop-helix

bHLH

basic domain helix-loop-helix

PKA

cAMP-dependent protein kinase

MBP

maltose binding protein

PAGE

polyacrylamide gel electrophoresis

EMSA

electrophoretic mobility shift assay

PVDF

polyvinylidene difluoride.
- Received November 12, 1996.
- Revision received February 5, 1997.