Cloning, characterization, and expression of the human TIN-ag-RP gene encoding a novel putative extracellular matrix protein

Activation of PI3K/AKT is involved in TINAG-mediated promotion of proliferation, invasion and migration of hepatocellular carcinoma

OBJECTIVE

Hepatocellular carcinoma (HCC) is a highly aggressive malignancy that has a poor prognosis. Through the literatures, TINAG significantly participated in the processes of the renal-associated diseases, but there were no studies about the roles of TINAG in the HCC development. Hence, we attempted to use the HCC samples collected by ourselves to reveal the clinical significance and prognostic impact of TINAG in HCC.

METHODS

We first measured the expression level of TINAG in HCC on the basis of TCGA database. Then, real time quantitative reverse transcription PCR (RT-qPCR) was used to examine the expression level of TINAG in 100 pairs of HCC tissues and corresponding adjacent non-tumor tissues, as well as HCC cell lines (HepG2, HB611, HHCC, and Hep3B). Moreover, Kaplan-Meier method and COX's proportional hazards model were utilized to perform the survival and prognosis analyses using the clinical data collected by ourselves. After knockdown of TINAG, the cell proliferation, invasion and migration capacities of HepG2 and Hep3B cells were evaluate by counting kit-8 (CCK-8) assay (24 h, 48 h, 72 h, and 96 h post-cultivation), clone formation experiment, would-healing, and invasion as well as migration assays. To further explore whether the dys-regulated TINAG expression regulates the HCC progression and prognosis, protein biomarkers of PI3K signaling pathway, including AKT, p-AKT, PI3K, p-PI3K, p70S6K, and p-p70S6K were measured based on western blotting analysis.

RESULTS

According to the data of TCGA database, clinical patients, and HCC cell lines, TINAG was highly expressed in HCC compared with normal. Relationship of TINAG expression level with the clinicopathological factors implicated that the high expression of TINAG was significantly associated with pathologic stage, pathologic-node, and pathologic-metastasis. Univariate as well as multivariate COX analysis indicated that TINAG expression and pathologic metastasis can serve as the independent prognostic factor for overall survival of HCC. After TINAG knockdown in HepG2 and Hep3B cells, cell proliferation rate, the colony numbers, and the invasive and migratory capacity were found to be suppressed. Remarkably, western blot results showed that reduction of TINAG remarkably decreased p-AKT, p-PI3K, and p-p70S6K expression level in HepG2 and Hep3B cells.

CONCLUSION

Collectively, our results underscore the significance of TINAG in HCC progression and prognosis, and TINAG might be a novel candidate oncogene in HCC. These results propose that targeting TINAG might offer future clinical utility in HCC.

Identification and characterization of the interactive proteins with cytotoxic T-lymphocyte antigen-2α

Cytotoxic T-lymphocyte antigen-2α (CTLA-2α) is a potent inhibitor of cathepsin L-like cysteine proteases. Recombinant CTLA-2α is known to be a potent, competitive inhibitor of cathepsin L-like cysteine proteases. In this study, cathepsin L, cathepsin C, and tubulointerstitial nephritis antigen-related protein 1 (TINAGL1) were identified as novel interactive proteins of CTLA-2α by the yeast two-hybrid screening system. The direct interactions and co-localization of these proteins with CTLA-2α were confirmed using co-immunoprecipitation and immunofluorescence staining, respectively. The disulfide-bonded CTLA-2α/cathepsin L complex was isolated from mouse tissue. CTLA-2α was found to be specific and consistently expressed on the maternal side of the mouse placenta. Double immunofluorescence analysis showed that CTLA-2α was co-localized with cathepsin L, cathepsin C, and TINAGL1 in placenta. A simple cell-based fluorescence assay revealed that CTLA-2α exhibited inhibitory activity toward cathepsin C in live cells, which indicated that CTLA-2α is a novel endogenous inhibitor of cathepsin C.

Role of extracellular matrix renal tubulo-interstitial nephritis antigen (TINag) in cell survival utilizing integrin (alpha)vbeta3/focal adhesion kinase (FAK)/phosphatidylinositol 3-kinase (PI3K)/protein kinase B-serine/threonine kinase (AKT) signaling pathway

Tubulo-interstitial nephritis antigen (TINag) is an extracellular matrix protein expressed in tubular basement membranes. Combined mutations in TINag and nephrocystin-1 genes lead to nephronophthisis with reduced cell survival. Because certain extracellular matrix proteins are known to modulate cell survival, studies were initiated in Lewis rats lacking TINag to assess if they are more susceptible to cisplatin-induced injury. Cisplatin induced a higher degree of tubular cell damage and apoptosis in regions where TINag is expressed in a parental Wistar strain. This was accompanied by an accentuated increase in serum creatinine and Kim-1 RNA and renal expression of Bax, p53, and its nuclear accumulation, mtDNA fragmentation, and a decrease of Bcl-2. Cisplatin induced fulminant apoptosis of HK-2 cells with increased caspase3/7 activity, mtDNA fragmentation, and a reduced cell survival. These effects were partially reversed in cells maintained on TINag substratum. Far Western/solid phase assays established TINag binding with integrin αvβ3 comparable with vitronectin. Transfection of cells with αv-siRNA accentuated cisplatin-induced apoptosis, aberrant translocation of cytochrome c and Bax, and reduced cell survival. The αv-siRNA decreased expression of integrin-recruited focal adhesion kinase (FAK) and p-FAK, while increasing the expression of p53 and p-p53. Similarly, p-AKT was reduced although ILK was unaffected. Inhibition of PI3K had similar adverse cellular effects. These effects were ameliorated in cells on TINag substratum. In vivo, a higher degree of decrease in the expression of p-FAK and pAKT was observed in Lewis rats following cisplatin treatment. These in vivo and in vitro studies demonstrate an essential role of TINag in cellular survival to maintain proper tubular homeostasis utilizing integrin αvβ3 and downstream effectors.

Interaction of human papillomavirus type 16 L2 with cellular proteins: identification of novel nuclear body-associated proteins

Two structural proteins form the Papillomavirus (PV) capsids. While the functions of the major structural protein L1 are well established, the exact functions for the minor structural protein L2 are much less well defined, except for some information on a role in viral entry and maturation of infectious virions. To gain more insight in the function of L2 we used the yeast two hybrid system with the Human Papillomavirus (HPV) 11 L2 and HPV16 L2 as bait proteins to isolate putative cellular interaction partners. We identified four proteins interacting with L2 proteins of at least two different HPV types and this interaction was confirmed in vitro by pull-down assays. Further evidence for this interaction was obtained by in vivo localization studies. Two of the proteins, the previously described PATZ and a novel protein, designated PLINP, were localized in discrete nuclear domains and colocalized with L2. The third protein, designated PMSP, is a newly identified cytoplasmic protein which was recruited to nuclear dots when coexpressed with L2. The fourth protein interacting with HPV16, 11 and 1 L2, the tubular-nephritis antigen related protein (TIN-Ag-RP), shows a cytoplasmic as well as a membrane bound subcellular distribution. Taken together, our data indicate that L2 of HPVs with different phenotypes interacts with several cellular host proteins, recruits one of them to the nucleus, and is complexed with at least three cellular proteins in specific nuclear domains. These findings suggest an HPV type-independent modulatory function of L2 on host-cell functions that involves discrete nuclear domains and alteration of the subcellular distribution of cellular proteins. The interacting cellular proteins identified may play a role in the viral life cycle and establishment of viral persistence.