**Core Concept**
The cytosolic cytochrome C is a key protein involved in the intrinsic mitochondrial pathway of apoptosis. It plays a crucial role in the activation of the caspase cascade, leading to programmed cell death.

**Why the Correct Answer is Right**
Cytosolic cytochrome C is released from the mitochondria into the cytosol during apoptosis. This release is triggered by the opening of the mitochondrial permeability transition pore (mPTP) and the activation of Bax and Bak, leading to the exposure of cytochrome C to the cytosol. Once in the cytosol, cytochrome C binds to Apaf-1, forming the apoptosome, which in turn activates caspase-9, initiating the caspase cascade and leading to cell death.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because cytosolic cytochrome C is not directly involved in the regulation of the cell cycle.
* **Option B:** This option is incorrect because cytochrome C is not a primary regulator of the heat shock response.
* **Option C:** This option is incorrect because cytosolic cytochrome C is not directly involved in the regulation of gene expression.

**Clinical Pearl / High-Yield Fact**
The release of cytochrome C from the mitochondria is a key event in the intrinsic pathway of apoptosis, and its inhibition can be a therapeutic target for cancer treatment.

**Correct Answer:** C.