Identification of a novel liver-specific expressed gene, TCP10L, encoding a human leucine zipper protein with transcription inhibition activity

TCP10L negatively regulates alpha-fetoprotein expression in hepatocellular carcinoma

Alpha-fetoprotein (AFP) is one of the most commonly used and reliable biomarkers for Hepatocellular carcinoma（HCC). However, the underlying mechanism of AFP expression in HCC is poorly understood. In this study, we found that TCP10L, a gene specifically expressed in the liver, is down-regulated in HCC and that its expression inversely correlates with AFP expression. Moreover, overexpression of TCP10L suppresses AFP expression whereas knockdown of TCP10L increases AFP ex-pression, suggesting that TCP10L might be a negative regulator of AFP. We found that TCP10L is associated with the AFP promoter and inhibits AFP promoter-driven transcriptional acti-vity. Taken together, these results indicate that TCP10L nega-tively regulates AFP expression in HCC and that it could be a potential prognostic marker and therapeutic target for HCC.

TCP10L synergizes with MAD1 in transcriptional suppression and cell cycle arrest through mutual interaction

T-complex protein 10A homolog 2 (TCP10L) was previously demonstrated to be a potential tumor suppressor in human hepatocellular carcinoma (HCC). However, little is known about the molecular mechanism. MAX dimerization protein 1 (MAD1) is a key transcription suppressor that is involved in regulating cell cycle progression and Myc-mediated cell transformation. In this study, we identified MAD1 as a novel TCP10L-interacting protein. The interaction depends on the leucine zipper domain of both TCP10L and MAD1. TCP10L, but not the interaction-deficient TCP10L mutant, synergizes with MAD1 in transcriptional repression, cell cycle G1 arrest and cell growth suppression. Mechanistic exploration further revealed that TCP10L is able to stabilize intracellular MAD1 protein level. Consistently, the MAD1-interaction-deficient TCP10L mutant exerts no effect on stabilizing the MAD1 protein. Taken together, our results strongly indicate that TCP10L stabilizes MAD1 protein level through direct interaction, and they cooperatively regulate cell cycle progression. [BMB Reports 2016; 49(6): 325-330]

TCP10L acts as a tumor suppressor by inhibiting cell proliferation in hepatocellular carcinoma

TCP10L (T-complex 10 (mouse)-like) has been identified as a liver and testis-specific gene. Although a potential transcriptional suppression function of TCP10L has been reported previously, biological function of this gene still remains largely elusive. In this study, we reported for the first time that TCP10L was significantly down-regulated in clinical hepatocellular carcinoma (HCC) samples when compared to the corresponding non-tumorous liver tissues. Furthermore, TCP10L expression was highly correlated with advanced cases exceeding the Milan criteria. Overexpression of TCP10L in HCC cells suppressed colony formation, inhibited cell cycle progression through G0/G1 phase, and attenuated cell growth in vivo. Consistently, silencing of TCP10L promoted cell cycle progression and cell growth. Therefore, our study has revealed a novel suppressor role of TCP10L in HCC, by inhibiting proliferation of HCC cells, which may facilitate the diagnosis and molecular therapy in HCC.

Identification of TCP10L as primate-specific gene derived via segmental duplication and homodimerization of TCP10L through the leucine zipper motif

TCP10L, a transcriptional repression factor gene that was localized on human chromosome 21q22.11, was identified to be derived through segmental duplication since the divergence of primates and rodents. It was elucidated that TCP10L gene was a primate-specific gene in this study. Subsequently it was demonstrated that the putative leucine zipper motif mediated the homodimerization of TCP10L. Using in vitro and in vivo methodologies, it was shown that either deletion or point mutation of the leucine zipper motif was sufficient to abolish TCP10L homodimerization. In Hela cells, both the exogenous wild type TCP10L and endogenous TCP10L were detected on nuclei with immunofluorescence assay. However, the leucine zipper motif mutants of TCP10L could also be detected on nuclei. The results suggested that the leucine zipper motif enabled TCP10L to homodimerize, but was not essential for the TCP10L nuclear localization.

TCP10L is expressed specifically in spermatogenic cells and binds to death associated protein kinase-3

The human transcriptional factor T-complex protein 10 like (TCP10L) gene is expressed exclusively in the liver and testis. However, the function of TCP10L in the testis remains unknown. We examined the expression of TCP10L in human testis and found that TCP10L was expressed specifically in the nucleus of spermatogenic cells during spermatogenesis. In addition, we identified death associated protein kinase 3 (DAPK-3/ZIP kinase) as a binding partner for TCP10L by yeast two-hybrid screening, followed with immunoprecipitation and subcellular localization experiments. Mutagenesis study revealed that this interaction was dependant on the leucine zipper motif-containing region. The specific expression pattern of TCP10L and interaction with DAPK-3 implies that TCP10L might play crucially important roles in spermatogenesis through its interaction with DAPK-3.