Final answer:
Once a signal triggers the expression of a transcriptional regulator, the protein activates the expression of its own gene by binding to specific regulatory DNA sequences.
Step-by-step explanation:
Once a signal triggers the expression of a transcriptional regulator, the transcriptional regulator protein itself activates the expression of its own gene. This is achieved by the transcriptional regulator protein binding to specific regulatory DNA sequences associated with its own gene. These DNA sequences, known as enhancers, turn on or increase gene transcription.
For example, in breast cancer, the overexpression of the epidermal growth factor receptor (EGFR) activates many protein kinases and transcription factors that control genes involved in cell growth.