12q23.1

APAF-1,CED4

Skin Cancers ( Melanoma, Basal Cell Carcinoma, Squamous Cell Carcinoma).

Frequent LOH in 12q22-23 locus (primary melanomas: 20-25% metastatic melanomas 35-40%).

The silencing of Apaf1 expression is often found in Melanomas. Two main mechanisms have been posited for APAF1 dimininution, either the allelic LOH in 12q22-23 locus and/or a transcriptional silencing by promoter methylation. The inactivation was not found in Nevi but it increased significantly in the later stages of carcinogenesis, when primary melanomas are fully developed (1-3mm of diameter). Very often such inactivation was associated with metastatic melanomas. Moreover, the APAF1 level is correlated with chemosensivity to different agents; different studies demonstrate that overexpressing or restoring a normal APAF1 level could sensitize chemoresistant melanoma cell lines, in vitro. Recently, APAF1 LOH determination on blood serum DNA has been proposed as a marker for selecting appropriate chemotherapy in stage IV melanoma patients.

Brain tumors (neural tumors, glial tumors)

Frequent LOH in 12q22-23 locus in glioblastomas (40%)

APAF1 seems to be downregulated or absent in Glioblastomas at mRNA and protein level. In addition, the co-overexpression of APAF1 and Caspase-9 sensitizes glioma cell lines (U-251 and U-373 MG) to p53-dependent apoptosis. Other modulations of the apoptosome-related apoptosis have been successfully conducted in order to induce apoptosis in glioma resistant lines. By contrast, APAF1 seems to be active in Neuroblastomas while there are no studies about a putative APAF1 role in other glial tumors (such as ependimoma, astrocytoma, ganglioglioma).

Head and neck cancers and odontogenic tumors.

There is no direct evidence of APAF1s role in the oncogenesis of these types of cancer even though Apaf1 loss has been correlated with gain of Cisplatin Chemoresistance in HSC-2CR cells (derived from HSC-2 head squamous carcinoma cells).

Gastro-intestinal tract cancers ( oesophagus cancer, gastric cancer, gallbladder cancer, ampulla of vater cancer, peritoneum cancer, vermiform appendix cancer, colon cancer, rectal cancer, cancer of the anus).

A low frequency of mutations (10-15 % of cases) is found in ColoRectal and Gastric Cancer. these mutations are due to the genetics of microsatellite instability and appear to be heterozygous. No evidences of APAF1 involvement have been found in the pathogenesis of the other tumors mentioned

Exocrinus pancreas cancers (various stages of the pancreas ductal adenocarcinoma - PDAC)

12q 1ocus deletions could be considered among the most frequent deletions in PDAC.

There is no direct evidence of APAF1 mutations in the progression of the PDAC (some even deny its possible role completely). There are many studies, however, which point out the 12q22-23 locus LOH or mutation in PDAC. Most of the mutated genes involved (such as K-Ras, p53, p16INK4a, p19ARF) can control the APAF1 level directly or indirectly throught the action of p53 and E2F-1 which both have active binding boxes to the APAF1 promoter.

Liver cancer and liver metastases

Methylation is a common feature in hepatocellular carcinoma (HCC) regulation. While the analysis of promoters methylation in HCC samples showed that the APAF1 gene is not hypermethylated, the HepG2 cells exposed to a demethylating agent (DEM, diethyl maleate) showed an increased level of Apaf1 and of some caspases which lead to G2 phase arrest and apoptosis.

Lung cancer

There is no direct evidence for abrogation of APAF1 function in lung cancer. However, the APAF1/Caspase-9 upregulation seem to be a protective mechanism in some NSCLC ( non small cell lung carcinoma) cell lines, while in other NSCLC lines (such as the NCI-H460) an indirect APAF1 loss of function is mediated by the upregulation of XIAP (an inhibitor of Apoptosome assembly). Furthermore, a driven expression of APAF1/ Caspase-9 (through the Inibition of XIAP in NCI-H460 cells or with low dose lung cancer cell lines) seems to augment sensitivity to death.

Tumors of the female reproductive organs ( ovarian carcinoma, neoplasms of Fallopian tube, endometrium, cervix, vulva and vagina)

In ovarian carcinoma, the APAF1 gene seems to be active. However, dysfunction in the apoptosome assembly process has been correlated with chemoresistance. In contrast, loss of heterozygosity was found in the apaf1 locus in malignant ovarian germ cell tumors. There is no information about the reproductive tract.

Tumors of the male reproductive organs ( seminoma, nonseminomatous germ cell tumors, sex cord-stromal tumors , other testis cancers, neoplasms of prostate, tumor of the penis)

Frequent deletions in Chromosome 12 long and short arm in germ line tumors; LOH in 12q22-23 is present in seminomas, non-seminomatous tumors and in mixed teratomas with various reported percentage (20-45%)

In Germ line tumors the APAF1 locus is often deleted; however it seems that APAF1 level was normal in various analyzed lines. Interestingly, Cisplatin treatment of a embryonal carcinoma cell line, TTSC-3 lead to the differentiation of the carcinoma through the up-regulation of pro-differentiation and pro-apoptotic genes (such as APAF1, Caspase-8 and TNFR1). In Prostatic Tumor there is no evidence of APAF1 involvement; however some studies have been conducted demontrating an increase of Apaf1 at transcription level as a cellular response to chemotherapeutic agents.

Urinary tract tumors ( renal cell carcinoma, neoplasms of the renal pelvis, ureter, bladder, urethra)

The Apoptosome function seems to be active in primary samples and in a few cell lines of Renal Cell Carcinoma. There are no informations about the urinary tract.

Hematopoietic system tumors.

Its not clear if APAF1 gene is corrupted in Leukaemias and Lymphomas. However, while the methylation of the promoter was demonstrated in different kinds of leukaemia, the protein level does not correlate with the messenger level, suggesting a multistep regulation in APAF1 expression. Furthermore, it has been demonstrated that the APAF1 overexpression, conducted by in vitro transfection or by chemoadiuvants, could overcome the resistance to chemo-radiotherapeutic agents.

Bone and soft tissue cancers (osteoma, sarcoma, fibroma, osteosarcoma)

There is no direct evidence of APAF1 role in the oncogenesis of these types of cancer even though in Ewings sarcoma cell lines the Apaf1 low level found in two different lines (STA-ET-2.1 and STA-ET-2.2) was correlated with chemoresistance to p53-dependent death stimuli compared with lines with normal APAF1 level. APAF1 was also absent and correlated with chemoresistance in the HT-1080 fibrosacroma cell line.

Various tumors ( eye tumor, heart and great vessels tumors, neoplasm of the endocrine glands and of the diffuse endocrine system, tumor of mesotheliums)

At present, there is no direct evidence of APAF1 involvement in the carcinogenesis of these neoplasms.