Cell Transformation, Cell Culture Techniques & Biosafety Levels Explained
Essay Question: Elaborate on Any Three Methods to Convert Normal Cells into Cancer Cells
Essay question: Elaborate on any three methods to convert normal cells into cancer cells
1. Chemical Carcinogens
Chemical agents trigger cancer by directly damaging DNA and forcing mutations in the specific genes responsible for managing cell division. As these genetic errors pile up, cells completely lose their brakes and begin dividing without limit. Scientists frequently apply these chemicals to cell cultures in labs to study how healthy cells turn malignant.
2. Viral Transformation
Certain viruses act as genetic intruders that rewrite a cell’s internal code. They achieve this by either inserting cancer-promoting genes (oncogenes) directly into the cell or by hijacking the cell’s existing genes to distort their behavior. When viral DNA welds itself into the host’s genetic blueprint, it knocks out normal regulation, leaving behind immortalized, fast-replicating cells.
3. Radiation-Induced Transformation
Ionizing radiation hits cells with high energy that physically shatters or alters DNA, leading to structural mutations and broken chromosomes. If this structural chaos strikes the genes that control cell life cycles, fix DNA errors, or trigger programmed cell death, the damaged cells escape their boundaries and take on cancerous traits.
Summary
Whether driven by chemicals, viruses, or radiation, the underlying trigger for cancer is always genetic damage. By breaking the systems that manage cell life and death, these factors unleash the chaotic, non-stop cell reproduction that defines cancer.
Which Enzyme Recruits DMSA?
Answer: DNA-dependent Protein Kinase (DNA-PK).
DNA-PK is a key enzyme in the non-homologous end joining (NHEJ) pathway and is recruited to DNA double-strand breaks to facilitate DNA repair.
What Is Cell Plasticity and How Can We Apply It in Fibroblasts?
Cell plasticity is the ability of a cell to change its phenotype or differentiate into another cell type in response to specific signals or environmental conditions.
Application in fibroblasts: Fibroblasts can be reprogrammed into other cell types. The lecture specifically discusses the reversion of fibroblasts to cardiomyocytes (heart muscle cells) through cellular reprogramming. This property is important in regenerative medicine, tissue repair, and cell-based therapies.
Biosafety Levels
BSL-1: Used for microorganisms that do not typically cause disease in healthy humans. Example: E. coli K-12 or Bacillus subtilis.
BSL-2: Used for moderate-risk organisms that can cause human disease. Examples: Salmonella spp., Staphylococcus aureus, and Hepatitis B virus.
BSL-3: Used for pathogens that can cause serious disease and may spread through the air. Examples: Mycobacterium tuberculosis and SARS coronavirus.
BSL-4: Used for highly dangerous and often fatal pathogens with no widely available treatment. Examples: Ebola virus and Marburg virus.
Chapter 1: Introduction to Cell Culture Technology
Definitions:
Cell Culture: Growing cells outside their natural environment under controlled conditions.
Adherent (Monolayer) vs. Suspension Culture: Adherent requires a solid surface or substrate; suspension grows free-floating in liquid medium.
Tissue Culture Types: Organ culture (3D structure maintained), Explant culture (outgrowth from tissue piece), Histotypic culture (reaggregated cells at high density), Organotypic culture (co-culturing different lineages).
Key Historical Milestones:
Sydney Ringer (19th C): Salt solution for organ survival.
Harrison & Roux (1885–1907): Hanging drop technique for frog embryo tissue.
Alexis Carrel (1910–1923): Tissue culture pioneer; organ transplantation.
Dr. George Gey (1951): Isolated HeLa cells (first continuous human cell line from Henrietta Lacks).
Equipment & Environment:
Incubation Conditions: 37°C, 2–5% CO2, 95% air, 99% humidity.
Laminar Flow Hoods: Horizontal (air facing operator; no user protection) vs. Vertical (downward air flow; protects user and sample).
Safety Hazards:
Teratogens: Gentamycin, Thapsigargin (SERCA ER Ca2+ pump inhibitor).
Carcinogens: Hygromycin.
Mutagens: Streptomycin.
Chapter 2: Biology of Cultured Cells
Isolation Protocol: Tissue excision → Mechanical/Enzymatic dissociation (Trypsin/Collagenase) → Filtration (0.22 µm) → Seeding at 1–2 x 10^5 cells/mL.
Primary Isolation Sequence
1. Tissue excision using a scalpel.
2. Mechanical disruption or enzymatic digestion using Trypsin or Collagenase.
3. Filtration through a 0.22 micron filter.
4. Cell counting on a hemocytometer (seed at 1 to 2 × 10^5 cells per mL).
5. Incubation in a CO2 incubator with media changes every 2 to 3 days until 80 percent confluent.
Substrate & Adhesion Molecules (CAMs)
Plastic Treatment: Polystyrene treated with high-energy ionizing radiation or electric ion discharge to create a charged surface.
Cadherins: Calcium-dependent cell-to-cell adhesion (adherens junctions, desmosomes).
Integrins: Heterodimers (α/β) for cell-substrate binding; recognizes the RGD motif (Arg-Gly-Asp) on Fibronectin, Laminin, Collagen.
Cell Cycle Regulators:
Positive Regulators: Cyclins, CDKs, Growth factors (PDGF, EGF, FGF).
Negative Regulators: p53, Rb, TGF-beta, CDK inhibitors (p21, p27).
Cell Cycle & Proliferation
Phases: M Phase (Mitosis) → G1 Phase (Restriction point) → S Phase (DNA Synthesis) → G2 Phase (Checkpoints and Apoptosis).
Stem Cells & Plasticity:
Totipotent: Forms all cell types + placenta (e.g., Zygote).
Pluripotent (PSCs): Forms all body layers (Endoderm, Mesoderm, Ectoderm) except placenta. Key factors: Oct4, Sox2, Nanog.
Fibroblast Reprogramming: Conversion to cardiomyocytes using Gata4, Mef2c, Tbx5.
Chapter 3: Basic Principles & Techniques in Cell Culture
Cell Morphology: Fibroblastic (elongated, adherent), Epithelial-like (polygonal, patches), Lymphoblast-like (spherical, suspension).
Culture Media:
Basal Media: Requires serum supplementation (e.g., DMEM, RPMI 1640).
Serum (FBS): Provides growth factors, hormones, lipids, trace elements, and pH buffering.
Serum-Free Media (SFM): Standardized formulation without animal serum.
Biosafety Levels (BSL)
BSL-1: Low risk; well-characterized non-pathogenic agents.
BSL-2: Moderate risk; human pathogens (most cell culture labs).
BSL-3: Aerosol transmitted pathogens; serious or lethal infections.
BSL-4: High individual risk; exotic, life-threatening viruses.
Cryopreservation Protocol Steps
1. Harvest log-phase cells with greater than 90 percent viability.
2. Resuspend in serum-containing media to inhibit trypsin.
3. Centrifuge and aspirate supernatant to collect cell pellet.
4. Add DMSO cryoprotectant to prevent ice crystal formation.
5. Perform slow freezing at −80°C.
6. Transfer to liquid nitrogen at −180°C for long-term storage.
Cell Quantification & Analysis:
Hemocytometer: Manual cell counting chamber using grid rules.
Automated Counters: High throughput, faster, precise cell counting.
Flow Cytometry / FACS: Laser-based cell analysis and sorting for biomarkers, cell cycle, apoptosis, and drug screening.
Chapter 4: Characterization of Cell Lines
Six Characterization Requirements:
1. Authentication: Confirming line is not cross-contaminated or misidentified.
2. Species Identification: Confirming donor species origin.
3. Tissue of Origin Correlation: Lineage markers and differentiation status.
4. Transformation Status: Finite vs. continuous status and malignancy properties.
5. Genetic Stability: Assessing karyotype and mutation drift.
6. Unique Identity: Unique characteristics vs. other strains.
Authentication Techniques:
STR Profiling: Standard short tandem repeat DNA profiling against databases (e.g., Cellosaurus) to detect cross-contamination.
Karyotyping: Chromosome number and structure analysis (Human: 46, Mouse: 40).
FISH: Detection of chromosomal rearrangements, amplifications, and deletions.
MSI Analysis: Microsatellite Instability testing for DNA mismatch repair defects.
Lineage Markers & Ploidy:
Astrocytes: GFAP (Glial fibrillary acidic protein).
Muscle Cells: Desmin, Myosin, Tropomyosin, CK-MM.
Neurons: Neurofilament protein, CK-BB.
DNA Dyes: Propidium Iodide (PI), DAPI, PicoGreen.
Chapter 5: Cell Transformation & Characteristics of Transformed Cells
Causes of Transformation: Spontaneous mutations, viral infection (SV40, HPV, EBV), gene transfection, chemical carcinogens, and UV radiation.
Molecular Mechanisms:
Point mutations in p53 (loss of apoptosis) or hyperactive KRAS.
Inactivation of Rb releasing E2F transcription factor.
Translocation in Burkitt’s Lymphoma: c-myc on Chromosome 8 translocates to Chromosome 14 next to the Ig heavy chain enhancer.
Four Hallmarks of Transformed Cells:
1. Genetic Instability: High mutation rate, aneuploidy, and heteroploidy.
2. Immortalization: Bypassing senescence via telomerase expression (hTERT) or viral oncogenes (SV40 Large T, HPV E6/E7).
3. Aberrant Growth Control: Anchorage independence, loss of contact inhibition, and low serum requirement.
4. Tumorigenicity: Ability to form tumors in vivo.