IDENTIFICATION OF 2 NOVEL ISOFORMS OF THE ZNF162 GENE - A GROWING FAMILY OF SIGNAL-TRANSDUCTION AND ACTIVATOR OF RNA PROTEINS

By differential screening of a cDNA library obtained from a GM-CSF-dep endent human myeloid leukemia cell line (GF-D8), we identified two nov el isoforms of the recently described ZNF162 gene, which is apparently linked to multiple endocrine neoplasia type 1. The shorter of these n ew isoforms, called B3, presents an open reading frame (ORF) of 1713 b p coding for 571 amino acids, its nucleotide sequence is homologous to the cDNA coding for the ABCDF isoform of ZNF162, except for a 4-nucle otide insertion that results in a frame shift of the ORF starting from nucleotide 1725 of the ZNF162 sequence. as a consequence, the predict ed translation product of B3 contains the consensus sequence of the A motif (G-X-X-X-X-G-K-S) of the ''ATP/GTP binding site,'' which is char acteristic of several protein families including protein kinases. More over, B3 shows the use of a different stop codon and contains a differ ent tyrosine-rich COOH terminus. The longer isoform, called B4, differ s from the ABCDEF isoform of ZNF162 by the insertion, at position 2137 , of 383 nucleotides leading to a different, proline-rich COOH terminu s. The complex transcription pattern of the ZNF162 gene is characteriz ed by four transcripts, of approximately 3.9, 3.7, 3.2, and 2.9 kb, in GF-D8 cells. The 3.7- and 2.9-kb transcripts are expressed in resting GF-D8 cells, Upon stimulation with GM-CSF the expression of these mRN As is up-regulated in parallel with the induction of two additional tr anscripts of 3.9 and 3.2 kb. The same pattern of expression has also b een observed in freshly isolated myeloid leukemia cells and normal CD3 4(+) stem cells. In light of these data, and since GM-CSF is known tee stimulate signal transduction pathways, it becomes relevant that all the different isoforms of ZNF162 contain the KB module, which is a seq uence motif present in proteins playing a major role in regulating cel lular RNA metabolism. A search for functional domains demonstrates tha t ZNF162 belongs to a new and growing family of genes dubbed STAR (sig nal transduction and activator of RNA) proteins that are thought to pl ay a downstream role in cell signaling and also in RNA binding. The ma mmalian members include Sam68, which is a target of Src, Fyn, and Grb2 , and the newly cloned mouse quaking proteins (qkI) necessary in early embryogenesis and myelination. Moreover, since ZNF162 is highly conse rved from yeast to humans, it implies that this new pathway has a sign ificant function. (C) 1997 Academic Press.