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Aberrant allele-specific replication, independent of parental origin, in blood cells of cancer patients.

Dotan ZA, Dotan A, Ramon J, Avivi L - BMC Cancer (2008)

Bottom Line: Malignancy was documented to be associated with gross modifications in the inherent replication-timing coordination between allelic counterparts of imprinted genes as well as of biallelically expressed loci.The non-disease specific aberrant epigenetic profile displayed in peripheral blood cells of patients with a solid tumour (unlike genetic aberrations) can be reversed, by an epigenetic drug applied in vitro, to the normal.It appears that the cancerous status differentiates between two allelic counterparts in a non-random manner, but independent of the parental origin.

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Affiliation: Department of Urology, Sheba Medical Center, Tel-Hashomer 52621, Israel. Zohar.Dotan@sheba.health.gov.il

ABSTRACT

Background: Allelic counterparts of biallelically expressed genes display an epigenetic symmetry normally manifested by synchronous replication, different from genes subjected to monoallelic expression, which normally are characterized by an asynchronous mode of replication (well exemplified by the SNRPN imprinted locus). Malignancy was documented to be associated with gross modifications in the inherent replication-timing coordination between allelic counterparts of imprinted genes as well as of biallelically expressed loci. The cancer-related allelic replication timing aberrations are non-disease specific and appear in peripheral blood cells of cancer patients, including those with solid tumors. As such they offer potential blood markers for non-invasive cancer test. The present study was aimed to gain some insight into the mechanism leading to the replication timing alterations of genes in blood lymphocytes of cancer patients.

Methods: Peripheral blood samples derived from patients with prostate cancer were chosen to represent the cancerous status, and samples taken from patients with no cancer but with benign prostate hyperplasia were used to portray the normal status. Fluorescence In Situ Hybridization (FISH) replication assay, applied to phytohemagglutinin (PHA)-stimulated blood lymphocytes, was used to evaluate the temporal order (either synchronous or asynchronous) of genes in the patients' cells.

Results: We demonstrated that: (i) the aberrant epigenetic profile, as delineated by the cancer status, is a reversible modification, evidenced by our ability to restore the normal patterns of replication in three unrelated loci (CEN15, SNRPN and RB1) by introducing an archetypical demethylating agent, 5-azacytidine; (ii) following the rehabilitating effect of demethylation, an imprinted gene (SNRPN) retains its original parental imprint; and (iii) the choice of an allele between early or late replication in the aberrant asynchronous replication, delineated by the cancer status, is not random but is independent of the parental origin.

Conclusion: The non-disease specific aberrant epigenetic profile displayed in peripheral blood cells of patients with a solid tumour (unlike genetic aberrations) can be reversed, by an epigenetic drug applied in vitro, to the normal. It appears that the cancerous status differentiates between two allelic counterparts in a non-random manner, but independent of the parental origin.

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SD values for SNRPN and CEN15 in cells of two groups of urology patients: (a) patients free of cancer (BPH); and (b) cancer patients (CAP). The values in each frame for each locus are presented in increasing order. P – the level of significance of the differences between the SNRPN and the CEN15 loci within a group of patients.
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Figure 2: SD values for SNRPN and CEN15 in cells of two groups of urology patients: (a) patients free of cancer (BPH); and (b) cancer patients (CAP). The values in each frame for each locus are presented in increasing order. P – the level of significance of the differences between the SNRPN and the CEN15 loci within a group of patients.

Mentions: The frequency of SD cells (see 'Cytogenetic evaluation' in Materials and Methods) for SNRPN was high in cells of the cancer-free urology patients, as expected for an imprinted region in normal samples. However, this very same locus in the samples of the cancer patients revealed low SD values, significantly lower (P < 10-11) than the expected values (Fig. 2; Table 1). In addition, the CEN15 alleles, which normally replicate synchronously, as seen here in the cells of the non-cancer patients (Fig. 2a), replicated highly asynchronously in the cells of the cancer patients, similar (P > 0.30) to the SNRPN in the cells of cancer-free patients (Fig. 2; Table 1). Thus, the cells of the cancer patients exhibited an abnormal mode of allelic replication: low SD values for SNRPN, which were significantly lower (P < 10-11) than the SD values obtained in the same samples for the CEN15 locus (Fig. 2b), and only slightly higher (P < 0.02) than the low SD value shown for CEN15 in the non-cancer samples (Fig. 2; Table 1). At the same time, the cells of the cancer-free urology patients exhibited the normal pattern of replication: high SD values for SNRPN and significantly lower (10-12) values for CEN15 (Fig. 2a).


Aberrant allele-specific replication, independent of parental origin, in blood cells of cancer patients.

Dotan ZA, Dotan A, Ramon J, Avivi L - BMC Cancer (2008)

SD values for SNRPN and CEN15 in cells of two groups of urology patients: (a) patients free of cancer (BPH); and (b) cancer patients (CAP). The values in each frame for each locus are presented in increasing order. P – the level of significance of the differences between the SNRPN and the CEN15 loci within a group of patients.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2629776&req=5

Figure 2: SD values for SNRPN and CEN15 in cells of two groups of urology patients: (a) patients free of cancer (BPH); and (b) cancer patients (CAP). The values in each frame for each locus are presented in increasing order. P – the level of significance of the differences between the SNRPN and the CEN15 loci within a group of patients.
Mentions: The frequency of SD cells (see 'Cytogenetic evaluation' in Materials and Methods) for SNRPN was high in cells of the cancer-free urology patients, as expected for an imprinted region in normal samples. However, this very same locus in the samples of the cancer patients revealed low SD values, significantly lower (P < 10-11) than the expected values (Fig. 2; Table 1). In addition, the CEN15 alleles, which normally replicate synchronously, as seen here in the cells of the non-cancer patients (Fig. 2a), replicated highly asynchronously in the cells of the cancer patients, similar (P > 0.30) to the SNRPN in the cells of cancer-free patients (Fig. 2; Table 1). Thus, the cells of the cancer patients exhibited an abnormal mode of allelic replication: low SD values for SNRPN, which were significantly lower (P < 10-11) than the SD values obtained in the same samples for the CEN15 locus (Fig. 2b), and only slightly higher (P < 0.02) than the low SD value shown for CEN15 in the non-cancer samples (Fig. 2; Table 1). At the same time, the cells of the cancer-free urology patients exhibited the normal pattern of replication: high SD values for SNRPN and significantly lower (10-12) values for CEN15 (Fig. 2a).

Bottom Line: Malignancy was documented to be associated with gross modifications in the inherent replication-timing coordination between allelic counterparts of imprinted genes as well as of biallelically expressed loci.The non-disease specific aberrant epigenetic profile displayed in peripheral blood cells of patients with a solid tumour (unlike genetic aberrations) can be reversed, by an epigenetic drug applied in vitro, to the normal.It appears that the cancerous status differentiates between two allelic counterparts in a non-random manner, but independent of the parental origin.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Urology, Sheba Medical Center, Tel-Hashomer 52621, Israel. Zohar.Dotan@sheba.health.gov.il

ABSTRACT

Background: Allelic counterparts of biallelically expressed genes display an epigenetic symmetry normally manifested by synchronous replication, different from genes subjected to monoallelic expression, which normally are characterized by an asynchronous mode of replication (well exemplified by the SNRPN imprinted locus). Malignancy was documented to be associated with gross modifications in the inherent replication-timing coordination between allelic counterparts of imprinted genes as well as of biallelically expressed loci. The cancer-related allelic replication timing aberrations are non-disease specific and appear in peripheral blood cells of cancer patients, including those with solid tumors. As such they offer potential blood markers for non-invasive cancer test. The present study was aimed to gain some insight into the mechanism leading to the replication timing alterations of genes in blood lymphocytes of cancer patients.

Methods: Peripheral blood samples derived from patients with prostate cancer were chosen to represent the cancerous status, and samples taken from patients with no cancer but with benign prostate hyperplasia were used to portray the normal status. Fluorescence In Situ Hybridization (FISH) replication assay, applied to phytohemagglutinin (PHA)-stimulated blood lymphocytes, was used to evaluate the temporal order (either synchronous or asynchronous) of genes in the patients' cells.

Results: We demonstrated that: (i) the aberrant epigenetic profile, as delineated by the cancer status, is a reversible modification, evidenced by our ability to restore the normal patterns of replication in three unrelated loci (CEN15, SNRPN and RB1) by introducing an archetypical demethylating agent, 5-azacytidine; (ii) following the rehabilitating effect of demethylation, an imprinted gene (SNRPN) retains its original parental imprint; and (iii) the choice of an allele between early or late replication in the aberrant asynchronous replication, delineated by the cancer status, is not random but is independent of the parental origin.

Conclusion: The non-disease specific aberrant epigenetic profile displayed in peripheral blood cells of patients with a solid tumour (unlike genetic aberrations) can be reversed, by an epigenetic drug applied in vitro, to the normal. It appears that the cancerous status differentiates between two allelic counterparts in a non-random manner, but independent of the parental origin.

Show MeSH
Related in: MedlinePlus