BRD4 is required for stimulating kinase activity of
**Core Concept**
BRD4 is a member of the BET (bromodomain and extra-terminal domain) family of proteins, which play a crucial role in regulating gene transcription by interacting with acetylated histones. Specifically, BRD4 is involved in the recruitment of the general transcription machinery to target gene promoters, thereby facilitating the initiation of transcription.
**Why the Correct Answer is Right**
BRD4 stimulates the kinase activity of CDK9 (Cyclin-Dependent Kinase 9), which is a key component of the P-TEFb (Positive Transcription Elongation Factor b) complex. This complex is essential for the phosphorylation and activation of the RNA polymerase II (RNAPII) enzyme, allowing for the elongation of transcription. By interacting with BRD4, CDK9 is recruited to target gene promoters, where it can phosphorylate and activate RNAPII, leading to the efficient transcription of genes.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because BRD4 does not stimulate the kinase activity of AKT (also known as Protein Kinase B), which is a serine/threonine kinase involved in cell survival and metabolism.
**Option B:** This option is incorrect because BRD4 does not stimulate the kinase activity of JAK2 (Janus Kinase 2), which is a tyrosine kinase involved in cytokine signaling.
**Option C:** This option is incorrect because BRD4 does not stimulate the kinase activity of mTOR (mechanistic Target Of Rapamycin), which is a serine/threonine kinase involved in cell growth and metabolism.
**Clinical Pearl / High-Yield Fact**
BRD4 is an attractive target for cancer therapy, as its inhibition has been shown to selectively kill cancer cells by disrupting their ability to undergo transcriptional elongation. Several small molecule inhibitors of BRD4 are currently in clinical trials for the treatment of various types of cancer.
**Correct Answer:** C.