Natural antisense transcripts of HIF-1α are conserved in rodents

Abstract

A natural antisense transcript (aHIF), which sequence is strictly complementary to the 3′ untranslated region (3′UTR) of HIF-1α mRNA, has been identified in human and shown to be overexpressed in renal carcinomas. We searched for aHIF in different rodent tissues. Two candidate expressed sequence tag (EST) were identified in silico and their PCR products (1.1 and 1.0 kb) were cloned and sequenced in mouse and rat, respectively. These transcripts were rigorously complementary to the 3′UTR of rodent HIF-1α mRNA and were broadly expressed in all mouse and rat tissues we tested. The conservation of aHIF in rodents underlined its potential importance in cell regulations. Therefore the responses of aHIF and HIF-1α transcripts were investigated in various types of hypoxic conditions. In freshly isolated rat renal tubules, aHIF RNA level was increased by acute hypoxia and low in normal supply of oxygen. In a rat strain raised in chronic hypobaric altitude hypoxia, aHIF transcript was greatly induced in the oxidative-type soleus and heart muscles of 3 month-old animals. By contrast, in the glycolytic-type extensor digitorum longus muscle aHIF transcript amount was lowered by hypoxia whereas HIF-1α transcript was highly expressed. In brain, where oxidative glycolysis takes place, HIF-1α mRNA and its antisense transcript levels were high and not significantly changed by altitude. Tumour cell lines cultured for 6 h in conditions mimicking hypoxia expressed lower amounts of HIF-1α mRNA. In two rat cell lines, aHIF transcript levels were greatly augmented after a 6-h incubation in these conditions, whereas in a mouse cell line, aHIF level was significantly reduced.