Functional regions of the homeodomain protein IDX-1 required for transactivation of the rat somatostatin genes

被引:53
作者
Lu, M [1 ]
Miller, CP [1 ]
Habener, JF [1 ]
机构
[1] HARVARD UNIV, HOWARD HUGHES MED INST,MASSACHUSETTS GEN HOSP, SCH MED,MOLEC ENDOCRINOL LAB, BOSTON, MA 02114 USA
关键词
D O I
10.1210/en.137.7.2959
中图分类号
R5 [内科学];
学科分类号
1002 ; 100201 ;
摘要
The insulin-, glucagon- and somatostatin-producing cells (beta, alpha and delta, respectively) in the pancreatic islets derive from a common precursor stem cell and differentiate sequentially during embryonic development. The homeodomain protein islet duodenum HOX (IDX)-1 [insulin promoter factor (IPF)-1/somatostatin transactivating factor (STF)-1)] is a transcription factor critically required for both the development of the pancreas and the transcriptional expression of the insulin gene. IDX-1 may also act to determine the differentiation of the common pancreatic precursor to beta, alpha and delta cells. Although IDX-1 is detected in most adult mouse islet beta-cells and regulates insulin gene transcription, it is also found in 158 of the delta-cells and transactivates the rat somatostatin gene. The roles of different domains of IDX-1 involved in the transactivation of the somatostatin gene are unclear. In this study, we have created a series of amino- and carboxy-terminal deletions, as well as point substitution mutations to delineate functional domains within the IDX-1 protein. We find that deletions amino-proximal to the homeodomain enhance DNA-binding to the TAAT-1 transcriptional control element within the somatostatin gene promoter. However, these amino-terminal deletions result in substantial decreases in transactivation of a transcriptional reporter containing the TAAT-1 element. Paradoxically, coexpression of the transcriptionally inactive, amino-terminally deleted IDX-1 mutant proteins, either with the wild-type IDX-1 or with themselves, results in a marked enhancement of transactivation of the transcriptional TAAT-1 element reporter. We provide evidence that this synergistic enhancement of transactivation is mediated by protein-protein interactions among the regions of IDX-1 located carboxyl-proximal to the homeodomain. Although successive deletions into the carboxyterminal region do not alter DNA-binding, these deletions result in a biphasic enhancement and diminution of transactivation. The IDX-1 homeodomain mediates sequence-specific DNA-binding because substitution mutations within this region abolish DNA-binding. All of the amino- and carboxy-terminal deletion proteins were present in nuclear extracts of transfected cells, suggesting that nuclear localization signals reside within the IDX-1 homeodomain. The mapping of the functional domains of IDX-1 may facilitate understanding of IDX-1-mediated gene regulation and islet cell development.
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页码:2959 / 2967
页数:9
相关论文
共 36 条
[1]   HYBRID INSULIN GENES REVEAL A DEVELOPMENTAL LINEAGE FOR PANCREATIC ENDOCRINE-CELLS AND IMPLY A RELATIONSHIP WITH NEURONS [J].
ALPERT, S ;
HANAHAN, D ;
TEITELMAN, G .
CELL, 1988, 53 (02) :295-308
[2]  
Ausubel F.M., 1992, SHORT PROTOCOLS MOL, V2nd
[3]   THE PITUITARY-SPECIFIC TRANSCRIPTION FACTOR-GHF-1 IS A HOMEOBOX-CONTAINING PROTEIN [J].
BODNER, M ;
CASTRILLO, JL ;
THEILL, LE ;
DEERINCK, T ;
ELLISMAN, M ;
KARIN, M .
CELL, 1988, 55 (03) :505-518
[4]   ANALYSIS OF SP1 INVIVO REVEALS MULTIPLE TRANSCRIPTIONAL DOMAINS, INCLUDING A NOVEL GLUTAMINE-RICH ACTIVATION MOTIF [J].
COUREY, AJ ;
TJIAN, R .
CELL, 1988, 55 (05) :887-898
[5]   HOMEO BOXES IN THE STUDY OF DEVELOPMENT [J].
GEHRING, WJ .
SCIENCE, 1987, 236 (4806) :1245-1252
[6]   THE CHICKEN PROGESTERONE-RECEPTOR - SEQUENCE, EXPRESSION AND FUNCTIONAL-ANALYSIS [J].
GRONEMEYER, H ;
TURCOTTE, B ;
QUIRINSTRICKER, C ;
BOCQUEL, MT ;
MEYER, ME ;
KROZOWSKI, Z ;
JELTSCH, JM ;
LEROUGE, T ;
GARNIER, JM ;
CHAMBON, P .
EMBO JOURNAL, 1987, 6 (13) :3985-3994
[7]  
GRUENEBERG DA, 1995, MOL CELL BIOL, V15, P3318
[8]  
GUZ Y, 1995, DEVELOPMENT, V121, P11
[9]   THE REGULATION OF TRANSCRIPTION BY PHOSPHORYLATION [J].
HUNTER, T ;
KARIN, M .
CELL, 1992, 70 (03) :375-387
[10]   A TISSUE-SPECIFIC TRANSCRIPTION FACTOR CONTAINING A HOMEODOMAIN SPECIFIES A PITUITARY PHENOTYPE [J].
INGRAHAM, HA ;
CHEN, R ;
MANGALAM, HJ ;
ELSHOLTZ, HP ;
FLYNN, SE ;
LIN, CR ;
SIMMONS, DM ;
SWANSON, L ;
ROSENFELD, MG .
CELL, 1988, 55 (03) :519-529