HTRF Human Total BCL-2 Detection Kit, 500 Assay Points

Total BCL-2 two-plate assay protocol

The two-plate protocol involves culturing cells in a 96-well plate before lysis, then transferring lysates into a 384-well low volume detection plate before the addition of total BCL-2 HTRF detection reagents. This protocol allows the cells' viability and confluence to be monitored.

Total BCL-2 one-plate assay protocol

Detection of total BCL-2 with HTRF reagents can be performed in a single plate used for culturing, stimulation, and lysis. No washing steps are required. This HTS designed protocol allows miniaturization while maintaining robust HTRF quality.

Validation of the specificity of total BCL-2 assay using HAP1 KO cell line

BCL-2 expression levels were assessed using the HTRF total BCL-2 kit in wild-type (WT), BCL-2 knockout (BCL-2 KO), and BCL-XL knockout (BCL-XL KO) HAP1 cell lines (100,000 cells/well).

The different cell lines were cultured in a 96-well plate for 24 h at 37°C and 5% CO₂. Cells were then lysed with supplemented Lysis Buffer #3 (1X), and 16 µL of cell lysate were transferred into a low-volume white microplate. Subsequently, 4 µL of premixed detection reagents were added. The HTRF signal was measured after a 3 h incubation at room temperature.

In BCL-2 KO HAP1 cells, the HTRF signal was reduced to the level of the non-specific signal, indicating a complete loss of BCL-2 expression. In contrast, BCL-2 was readily detected in both WT and BCL-XL KO cell lines.

These results demonstrate the high selectivity of the HTRF total BCL-2 kit, which specifically detects BCL-2 protein with no detectable cross-reactivity to the closely related BCL-XL family member under the tested conditions.

Assessment of total BCL-2 levels in various cell lines

THP-1, Jurkat, SH-SY5Y, MCF-7, and HAP1 cells were seeded at 100,000 cells/well in a 96-well microplate. After overnight incubation, cells were lysed with supplemented Lysis Buffer #3, and 16 µL of lysate were transferred into a low-volume 384-well white microplate. Subsequently, 4 µL of HTRF total BCL-2 detection reagents were added. The HTRF signal was measured after a 3 h incubation at room temperature.

The HTRF total BCL-2 assay supports the robust detection of endogenous BCL-2 across a variety of cellular models expressing different levels of the protein, demonstrating its applicability across multiple cellular models for cell-based studies.

BCL-2 signaling pathway

B-cell lymphoma 2 (BCL-2) is a key regulator of cell survival and apoptosis through the mitochondrial (intrinsic) apoptotic pathway. Under physiological conditions, BCL-2 is primarily localized on the outer mitochondrial membrane, endoplasmic reticulum, and nuclear envelope, where it helps maintain cellular homeostasis by preserving mitochondrial integrity and preventing apoptosis.

BCL-2 expression and activity are regulated by several signaling pathways. Activation of receptor tyrosine kinases stimulates the PI3K/AKT pathway, leading to increased BCL-2 expression through transcription factors such as CREB and NF-κB, thereby enhancing cellular resistance to apoptotic stimuli. In addition, activation of the NF-κB pathway by inflammatory cytokines, growth factors, or cellular stress promotes BCL-2 transcription and supports cell survival. Growth factor-mediated activation of the MAPK/ERK pathway can further enhance the anti-apoptotic function of BCL-2 through phosphorylation-dependent stabilization.

As an anti-apoptotic protein, BCL-2 prevents mitochondrial outer membrane permeabilization (MOMP) by binding to and sequestering the pro-apoptotic effector proteins BAX and BAK, thereby preventing their oligomerization within the mitochondrial membrane. Consequently, the release of cytochrome c and other apoptogenic factors into the cytosol is blocked, suppressing caspase activation and apoptosis. BCL-2 also binds to and neutralizes BH3-only proteins such as BIM, BID, PUMA, NOXA, and BAD, which are normally activated in response to cellular stress and promote BAX/BAK activation.

In response to severe cellular damage or prolonged stress, several mechanisms antagonize BCL-2 activity. The tumor suppressor p53 induces the expression of pro-apoptotic genes, including BAX, PUMA, and NOXA, shifting the balance toward apoptosis. Additionally, stress-activated kinases such as JNK can phosphorylate BCL-2, reducing its anti-apoptotic function. When BCL-2-mediated protection is overcome, BAX and BAK oligomerize within the mitochondrial membrane, triggering MOMP, cytochrome c release, apoptosome formation, caspase activation, and ultimately programmed cell death.

Dysregulation of BCL-2 is frequently observed in cancer, where BCL-2 overexpression promotes tumor cell survival and resistance to therapy. Consequently, BCL-2 has become an important therapeutic target, exemplified by the development and clinical investigation of selective BCL-2 inhibitors such as venetoclax in hematological malignancies.