RRP22: a novel neural tumor suppressor for astrocytoma

Astrocytomas are the most common neoplasm of the central nervous system. Although progress has been made, the survival rate of astrocytoma is still poor. Therefore, improving the prognosis of patients with astrocytomas relies on effective therapies that are directed against unique molecular aberrations. Previous studies have revealed that a novel member of the Ras superfamily, RRP22, which is located on chromosome 22 on the 12q site, is exclusively expressed in the central nervous system. RRP22 can be modified by farnesyl and down-regulated in a variety of neural tumor cell lines. In this study, we analyzed the mRNA level of RRP22 in normal brain tissues and astrocytomas using quantitative RT-PCR. Our results showed that the mRNA level in astrocytomas was significantly down-regulated compared to levels in normal tissues. As the pathological grade (World Health Organization (WHO) classification 2007) increased, the expression of RRP22 decreased. However, according to our research, there was no significant difference between malignant astrocytomas with pathological grades of III or IV. To investigate the possible effects of RRP22 on the biological behavior of glioma cells, we transfected RRP22 into a malignant cell line of astrocytomas, U251. We found that RRP22 inhibited growth, decreased invasiveness, and induced cell death. Thus, RRP22 is a special neural tumor suppressor for human astrocytomas, although further studies are needed to define the detailed mechanisms.