84513

PPAPDC1B

phosphatidic acid phosphatase type 2 domain containing 1B;PPAPDC1B;phosphatidic acid phosphatase type 2 domain containing 1B

diacylglycerol pyrophosphate like 1|phosphatidate phosphatase PPAPDC1B|phosphatidic acid phosphatase type 2 domain-containing protein 1B

8p11.23

protein-coding

Our previous studies suggested that chromosome 8p deletion is associated with metastasis of hepatocellular carcinoma (HCC), in which some novel metastasis suppressor genes might be harbored. The present study aimed to identify the metastatic suppressor gene(s). A cDNA chip was constructed with the expressed sequence tags (ESTs) from chromosome 8p and used to compare the difference of expression profiling between the MHCC97-H and MHCC97-L cell lines with different metastatic potentials and similar genetic backgrounds. In all, 10 ESTs were significantly downregulated in MHCC97-H cell line with higher metastatic potential. One full-length gene, HTPAP (phosphatidic acid phosphatase type 2 domain containing 1B), was identified at chromosome 8p12. Sequencing and bioinformatic analyses revealed that HTPAP has 826 bp and encodes a putative protein of 175 amino acids with a transmembrane segment at the NH2 terminus, two protein kinase C phosphorylation site and one tyrosine kinase phosphorylation site. Its expression level in metastatic tumor tissues was much lower than that of primary HCC tissues. Both in vitro and in vivo assays suggested that HTPAP could suppress the invasion and metastasis of HCC. These suggested that HTPAP is a novel metastatic suppressor gene for HCC. The mechanism of the effect of HTPAP on HCC metastasis is not clear yet and deserves further investigation.

Our previous study has identified HTPAP as a novel metastasis suppressor from chromosome 8p which is often deleted in metastatic HCC. We sought to further evaluate the expression levels of transcript variants of HTPAP (HTPAP-1, HTPAP-2 and HTPAP-3) in 67 HCC tumor tissues and 11 normal liver tissues by RT-PCR with specific TaqMan probes and primer sets, and explore their association with HCC metastasis and survival. We found that the expression levels of three HTPAP transcript variants were quite different in HCCs. Only HTPAP-1 was found to be significantly associated with HCC metastasis (P=0.00053), overall survival (P=0.0023) and time to recurrence (P=0.010) of HCC. Patients with a lower expression of HTPAP-1 were inclined to accompany intrahepatic metastases and tumor thrombi (P<0.05) and had a poor prognosis. In vitro, three fusion pEGFP-N1 vectors encoding HTPAP-1, HTPAP-2 and HTPAP-3 were introduced into HCC cells respectively to track HTPAPs' expressions and identify their function. We found overexpression of HTPAP-1 conferred HCC cells reduced ability of invasion without significant impact on cell proliferation, and also displayed a distinct cell location on cell membrane and in cytoplasm, which were different from two other variants. Consequently, HTPAP-1 may be the transcript of HTPAP to exhibit a suppressive role on HCC metastasis, and can be a prognostic marker for HCC.

The phosphatidic acid phosphatase HTPAP has been defined as a metastatic suppressor of hepatocellular carcinoma (HCC), but little is known about its function or potential applications as a prognostic marker. In this study, we analyzed patterns of HTPAP genetic variation and gene expression in 864 patients who underwent HCC resection, assessing these patterns for correlations to tumor metastasis potential. Focusing on two tagSNPs that were selected (+357G/C and +1838A/G), we found that only the +357G/C genotype was significantly associated with HTPAP mRNA and protein expression levels and the probability of metastasis. In an independent cohort of 665 HCC patients, we determined that the +357G/C genotype was associated with shorter time to recurrence and overall survival. Together, these results indicated that the HTPAP tagSNP +357 GG+GC genotypes may influence HCC metastatic potential and clinical prognosis by down-regulating HTPAP expression. Extending these results, a global expression profiling analysis identified 41 genes including the pro-inflammatory genes IL-8 and TLR2 that were significantly overexpressed in the +357 GG+GC group, as possible coregulated markers with HTPAP. Together, our findings identify an HTPAP genotype and associated gene expression pattern that favors metastasis progression and that could be used to predict tumor metastasis and prognosis in HCC patients.