28. The following statements have been proposed for a cancer cell.
    A. Binding of p53 with MDM2, a ubiquitin E3 ligase; is a precondition for cancer progression.
    B. Phosphorylation of a tyrosine residue in the C- terminus of human c-Src is essential for cell invasion and motility.
    C. Loss of function of both alleles of a tumor Suppressor gene prevents metastasis.
    D. Dimerization of C-myc-Max leads to enhanced cell proliferation.
    Which of the combinations of the above statements is correct?
    (1) A and B (2) C and D
    (3) A and D (4) B and C

The correct combination of statements related to cancer cells is:

(2) C and D

Explanation:

• Statement A: Binding of p53 with MDM2, a ubiquitin E3 ligase, is not a precondition for cancer progression. Instead, MDM2 negatively regulates p53 by ubiquitination and proteasomal degradation, controlling p53 levels. Overexpression of MDM2 can inhibit p53 tumor suppressor activity, facilitating cancer progression, but the mere binding is not itself a prerequisite for cancer progression.​

• Statement B: Phosphorylation of a tyrosine residue in the C-terminus of human c-Src is indeed essential for cell invasion and motility. Src is a tyrosine kinase involved in signaling pathways regulating cell motility and invasion [general knowledge].

• Statement C: Loss of function of both alleles of a tumor suppressor gene typically promotes metastasis or tumorigenesis. Saying it prevents metastasis is incorrect. So this statement as it stands is generally incorrect.

• Statement D: Dimerization of c-Myc with Max leads to enhanced cell proliferation since the c-Myc-Max complex functions as a transcription factor that activates genes promoting cell cycle progression and growth.

Therefore, B and D are correct, but only the options given are (1) A and B, (2) C and D, (3) A and D, (4) B and C, and among these, the best fitting correct combination is (1) A and B if exclusively considering Src phosphorylation and MDM2-p53 binding relevance. However, re-evaluating the statement on C and D:

• Statement C says “Loss of function of both alleles of a tumor suppressor gene prevents metastasis” which is incorrect—loss promotes tumorigenesis and metastasis.

• Therefore, (1) A and B is the correct choice.

Summary:

• MDM2-p53 binding negatively regulates p53 but is part of cancer progression.

• Src phosphorylation is essential for invasion.

• c-Myc-Max dimerization enhances proliferation (partially true but no option pairs with A and D excluding C).

• Loss of tumor suppressor function promotes cancer, not prevents it.

Thus, (1) A and B aligns best with current knowledge.