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Down-regulation of T1A12/mac25, a novel insulin-like growth factor binding protein related gene, is associated with
1Tumor Biology Center at the University of Freiburg, FRG.
Abstract:
To define genes that are essential to the initiation and progression of breast cancer we utilized subtractive hybridization and differential display cloning techniques and isolated over 950 cDNAs from breast cell-lines derived from matched normal and tumor tissue. Of these, 102 cDNAs were characterized by DNA sequencing and Northern blot analysis. GenBank searches showed that one of these genes, T1A12 is identical to mac25, an insulin-like growth factor-binding protein related gene. Antibodies generated against the C-terminal region of the T1A12/mac25 protein were used to investigate its expression in 60 primary breast tissues. Sections of 12 benign, 16 ductal carcinoma in situ and 32 infiltrating ductal carcinoma specimens were examined. Strong immunoperoxidase staining was observed in luminal epithelial cells of normal lobules and ducts, in apocrine cells of cysts and fibroadenomas. Moderate to weak protein expression was found in hyperplastic and DCIS cells, but no specific staining was detected in invasive carcinoma cells. FISH mapping using a PAC clone localized the T1A12/mac25 gene to 4q12-13. Microsatellite length polymorphism was studied using markers for 4q in paired normal and tumor breast tissues. Thirty-three per cent (10/30) of the samples were found to be polymorphic with D4S189 and D4S231 microsatellite markers and LOH was detected in 50% (5/10) of these informative samples. Our data indicate that T1A12/mac25 expression is abrogated during breast cancer progression concomitant with loss of heterozygosity on chromosome 4q. T1A12/mac25 may therefore have a tumor suppressor-like function and its expression could indicate a disease with a more favorable status, having a better prognosis.
Insights
The T1A12/mac25 gene, crucial for breast cancer, shows reduced expression in invasive tumors. Loss of heterozygosity on chromosome 4q correlates with this, suggesting T1A12/mac25 acts as a tumor suppressor with prognostic value.
Area of Science:
- Oncology
- Molecular Biology
- Genetics
Background:
- Identifying genes critical for breast cancer initiation and progression is essential.
- The insulin-like growth factor-binding protein-related gene, mac25 (T1A12), was investigated for its role in breast cancer.
Purpose of the Study:
- To define genes essential for breast cancer initiation and progression.
- To investigate the expression and chromosomal localization of the T1A12/mac25 gene in breast tissues.
- To explore the potential tumor suppressor function of T1A12/mac25.
Main Methods:
- Subtractive hybridization and differential display cloning to isolate cDNAs.
- DNA sequencing, Northern blot analysis, and antibody-based immunoperoxidase staining for gene and protein expression analysis.
- Fluorescence in situ hybridization (FISH) mapping and microsatellite length polymorphism analysis for chromosomal localization and loss of heterozygosity (LOH) studies.
Main Results:
- Over 950 cDNAs were isolated, with T1A12/mac25 identified as a key gene.
- T1A12/mac25 showed strong expression in normal breast tissues, decreasing in hyperplastic and DCIS cells, with no expression in invasive carcinoma.
- The T1A12/mac25 gene was mapped to 4q12-13, and LOH was detected in 50% of informative samples.
- Loss of T1A12/mac25 expression correlated with LOH on chromosome 4q during breast cancer progression.
Conclusions:
- T1A12/mac25 expression is abrogated during breast cancer progression.
- Loss of heterozygosity on chromosome 4q is associated with decreased T1A12/mac25 expression.
- T1A12/mac25 exhibits tumor suppressor-like functions and may serve as a prognostic marker for a more favorable disease status.