Prep1 controls insulin glucoregulatory function in liver by transcriptional targeting of SHP1 tyrosine phosphatase.
We investigated the function of the Prep1 gene in insulin-dependent glucose homeostasis in liver.



Prep1 action on insulin glucoregulatory function has been analyzed in liver of Prep1-hypomorphic mice (Prep1(i/i)), which express 2-3% of Prep1 mRNA.



Based on euglycemic hyperinsulinemic clamp studies and measurement of glycogen content, livers from Prep1(i/i) mice feature increased sensitivity to insulin. Tyrosine phosphorylation of both insulin receptor (IR) and insulin receptor substrate (IRS)1/2 was significantly enhanced in Prep1(i/i) livers accompanied by a specific downregulation of the SYP and SHP1 tyrosine phosphatases. Prep1 overexpression in HepG2 liver cells upregulated SYP and SHP1 and inhibited insulin-induced IR and IRS1/2 phosphorylation and was accompanied by reduced glycogen content. Consistently, overexpression of the Prep1 partner Pbx1, but not of p160MBP, mimicked Prep1 effects on tyrosine phosphorylations, glycogen content, and on SYP and SHP1 expression. In Prep1 overexpressing cells, antisense silencing of SHP1, but not that of SYP, rescued insulin-dependent IR phosphorylation and glycogen accumulation. Both Prep1 and Pbx1 bind SHP1 promoter at a site located between nucleotides -2,113 and -1,778. This fragment features enhancer activity and induces luciferase function by 7-, 6-, and 30-fold, respectively, in response to Prep1, Pbx1, or both.



SHP1, a known silencer of insulin signal, is a transcriptional target of Prep1. In liver, transcriptional activation of SHP1 gene by Prep1 attenuates insulin signal transduction and reduces glucose storage.
Oriente
Francesco
F
Dipartimento di Biologia e Patologia Cellulare e Molecolare, Istituto di Endocrinologia ed Oncologia Sperimentale del Consiglio Nazionale delle Ricerche, Università degli Studi di Napoli Federico II, Naples, Italy.
Iovino
Salvatore
S
Cabaro
Serena
S
Cassese
Angela
A
Longobardi
Elena
E
Miele
Claudia
C
Ungaro
Paola
P
Formisano
Pietro
P
Blasi
Francesco
F
Beguinot
Francesco
F
D000818:Animals; D002460:Cell Line; D017931:DNA Primers; D004041:Dietary Fats / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism; D056945:Hep G2 Cells / Q000378:metabolism; D018398:Homeodomain Proteins / Q000235:genetics*; D006801:Humans; D007328:Insulin / Q000502:physiology*; D008099:Liver / Q000201:enzymology / Q000378:metabolism / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D009841:Oligonucleotides / Q000737:chemistry; D010957:Plasmids / Q000235:genetics; D000075062:Pre-B-Cell Leukemia Transcription Factor 1; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11 / Q000235:genetics; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6 / Q000235:genetics* / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D014157:Transcription Factors / Q000235:genetics; D014158:Transcription, Genetic; D014280:Triglycerides / Q000378:metabolism
D017931:DNA Primers; D004041:Dietary Fats; D018398:Homeodomain Proteins; D007328:Insulin; D009841:Oligonucleotides; C481797:Pbx1 protein, mouse; C491412:Pknox1 protein, mouse; D000075062:Pre-B-Cell Leukemia Transcription Factor 1; D014157:Transcription Factors; D014280:Triglycerides; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; C516725:Ptpn11 protein, mouse; D005947:Glucose