Impaired RNA splicing of 5 '-regulatory sequences of the astroglial glutamate transporter EAAT2 in human astrocytoma

A loss of the glutamate transporter EAAT2 has been reported in the neoplast ic transformation of astrocytic cells and astrocytoma. The RNA expression o f EAAT2 and five 5'-regulatory splice variants was investigated to identify alterations of the post-transcriptional EAAT2 gene regulation in human ast rocytic tumours. Three known (EAAT2, HBGTII, and HBGTIIC) and two novel (EAAT2/3 and EAAT2/3 1) EAAT2 transcripts originating from alternative splicing of 5'-regulatory sequences were subject to an RNA expression analysis using reverse transcr iption and competitive PCR. Specimens of astrocytoma World Health Organisat ion (WHO) grade I-IV in 14 patients and control brain tissue obtained from three normal persons were studied. The main EAAT2 RNA was found to be equally expressed in normal human brain and astrocytic tumour samples. By contrast, the expression pattern of four 5'-variants of the transporter transcript was altered in the investigated s eries of astrocytoma compared with normal brain. HBGTII, HBGTIIC, and EAAT2 /3 were amplified from seven and four tumours and one sample, respectively. EAAT2/31 was expressed in none of the tumour specimens studied. In conclusion, in astrocytic. tumours of different histopathological grades there was a substantial reduction of RNA splicing events in EAAT2. The imp airment of EAAT2 splicing indicates an altered expression which is not prim arily involved in the tumorigenesis but may contribute to some biological p roperties of astrocytoma such as oedema, necrosis, and tumour related seizu res.