Cyclin D1 (PRAD1) alternative transcript b: full-length cDNA cloning and expression in breast cancers

Area of Science:

• Molecular Biology
• Oncology
• Cell Cycle Regulation

Background:

• The cyclin D1/PRAD1 protooncogene is crucial for cell cycle G1 phase regulation and implicated in human tumor development.
• A novel alternatively spliced cyclin D1 transcript, termed transcript b, has been identified, featuring altered C-terminus due to splicing failure at exon 4.
• Previous studies could not differentiate between cyclin D1 transcript variants due to similar sizes, leaving their roles in tumors unknown.

Purpose of the Study:

• To isolate and sequence the coding region of the novel cyclin D1 transcript b.
• To determine the expression levels of cyclin D1 transcript a and transcript b in human breast cancers and cell lines.

Main Methods:

• cDNA cloning of the variant transcript b from breast cancer cell lines.
• Northern blot analysis and reverse transcription-polymerase chain reaction (RT-PCR) to quantify transcript levels.

Main Results:

• The complete coding sequence of cyclin D1 transcript b was determined, predicting a 274-amino acid protein lacking a C-terminal PEST sequence.
• Both transcript a and transcript b were detected in primary breast cancers and cell lines.
• Transcript b was found at significantly lower levels than transcript a in all samples analyzed.

Conclusions:

• While cyclin D1 transcript b is expressed in breast cancer, its low abundance suggests transcript a is predominantly responsible for oncogenic overexpression.
• The specific role of cyclin D1 transcript b in oncogenesis requires further investigation.