Evidence of a noncoding transcript of theRIPK2gene overexpressed in head and neck tumor

Abstract

39Receptor-interacting proteins are a family of serine/threonine kinases, which integrate 40 extra and intracellular stress signals caused by different factors, including infections, 41 inflammation and DNA damage. Receptor-interacting serine/threonine-protein kinase 2 (RIP-42 2) is a member of this family and an important component of the nuclear factor NF-kappa-B 43 signaling pathway. The corresponding human gene RIPK2 generates two transcripts by 44 alternative splicing, the full-length and a short transcript. The short transcript has a truncated 45 5' sequence, which results in a predicted isoform with a partial kinase domain but able to 46 transduce signals through its caspase recruitment domain. In this study, the expression of 47 RIPK2 was investigated in human tissue samples and, in order to determine if both transcripts 48 are similarly regulated at the transcriptional level, cancer cell lines were submitted to 49 temperature and acid stresses. We observed that both transcripts are expressed in all tissues 50 analyzed, with higher expression of the short one in tumor samples, and they are differentially 51 regulated following temperature stress. Despite transcription, no corresponding protein for the 52 short transcript was detected in tissues and cell lines analyzed. We propose that the shorter 53 transcript is a noncoding RNA and that its presence in the cell may play regulatory roles and 54 affect inflammation and other biological processes related to the kinase activity of RIP-2. Villagra et al 3 3 56 Introduction 57Unicellular and multicellular organisms are constantly exposed to stressful 58 environments. Chemical and physical stimuli trigger different adaptive responses, which will 59 determine the capability of the organism to maintain internal homeostasis [1]. 60 Receptor-interacting proteins (RIP) are a family of serine/threonine kinases, which 61 integrate extra-and intracellular stress signals and share a homologous kinase domain at the 62 N-terminus, but have different C-terminal functional domains [2-4]; RIP-2 (receptor-63 interacting serine/threonine-protein kinase 2) is a member of the RIP family, which has 64 received attention in the recent years for its role in modulating immune and inflammatory 65 processes [5], and as a sensor of cellular stress [6]. It is expressed at high levels in several 66 normal human tissues [7], as well as in pathological conditions, for example ulcerative colitis 67 [8], triple-negative breast cancers [9,10] and in stressful conditions, such as after 68 hypoxic/ischemic insults [11]. Conversely, lower levels of RIP-2 have been correlated with 69 tumor progression in squamous cell carcinoma (SCC) of the oral cavity [12]. 70RIP-2 is the only member of the RIP family that besides phosphorylating serines and 71 threonines is able to autophosphorylate tyrosine residues [13,14]. Its ATP-and substrate 72 binding sites spread over much of the N-terminal kinase domain, and a caspase recruitment Fig 1A). CARD 74 specifically interacts with the nucleotide-bind...