Expression of Truncated Products at the 5'-Terminal Region of RIPK2 and Evolutive Aspects that Support Their Biological Importance.

Alternative splicing is the process of generating different mRNAs from the same primary transcript, which contributes to increase the transcriptome and proteome diversity. Abnormal splicing has been associated with the development of several diseases including cancer. Given that mutations and abnormal levels of the RIPK2 transcript and RIP-2 protein are frequent in tumors, and that RIP-2 modulates immune and inflammatory responses, we investigated alternative splicing events that result in partial deletions of the kinase domain at the N-terminus of RIP-2. We also investigated the structure and expression of the RIPK2 truncated variants and isoforms in different environments. In addition, we searched data throughout Supraprimates evolution that could support the biological importance of RIPK2 alternatively spliced products. We observed that human variants and isoforms were differentially regulated following temperature stress, and that the truncated transcript was more expressed than the long transcript in tumor samples. The inverse was found for the longer protein isoform. The truncated variant was also detected in chimpanzee, gorilla, hare, pika, mouse, rat, and tree shrew. The fact that the same variant has been preserved in mammals with divergence times up to 70 million years raises the hypothesis that it may have a functional significance.

Sequence and transcriptional study of HNRPK pseudogenes, and expression and molecular modeling analysis of hnRNP K isoforms.

The heterogeneous nuclear ribonucleoproteins (hnRNPs) comprise a large family of proteins that play important roles in telomere biogenesis, DNA repair, cellular signaling, and the regulation of expression at both the transcriptional and translational levels. One of the most extensively studied hnRNP family members, hnRNP K, has been implicated in a variety of processes, including chromatin remodeling, transcription, splicing, and translation events. In this study, we analyzed processed HNRPK pseudogenes (HNRPK psi1-psi4) and coding sequences. HNRPK pseudogenes are apparently nonfunctional, and psi1 might correspond to transcripts from an ancestral gene. Phylogenetic and sequence analyses suggest that HNRP genes arose by duplication, and that new structural and sequence features expanded the functions of hnRNPs. The expression analysis of hnRNP K isoforms showed that isoform a is expressed in normal testis and in non-small cell lung cancer (NCI-H1155 NSCLC cell line), although the shorter isoform (isoform b) is expressed in different tumor cell lines (IM9 B-lymphoblastoid, Hs578T human breast cancer epithelial, T98G human glioma cell lines). Using molecular modeling, we obtained KH1 and KH3 models, which pointed to important residues for DNA-protein binding and no structural differences between isoforms a and b. To our knowledge, this is the first phylogenetic study including vertebrate HNRP genes and HNRPK pseudogenes, and the first report comparing the KH1 and KH3 domains of isoforms a and b of the hnRNP K protein. New investigations in tumor samples must be done to validate the differential expression observed here. The results shown are important because the hnRNP K protein might represent a new target for pharmacologic intervention in virus replication and cancer.