Answer to Question #246872 in Biochemistry for Noob

Question #246872

How can I answer something like this?

The laboratory of your PhD supervisor has developed a DNA aptamer that that has been designed to bind the epidermal growth factor receptor (EGFR). Preliminary evidence indicates that the aptamer binds and prevents epidermal growth factor from binding, but a bivalent form of the aptamer (two aptamers linked together) acts as an EGFR agonist. You have access to the human glioma cell line U87 that overexpresses EGFR, and a null-mutant of the same cell line that carries a non-functional EGFR. Describe a series of experiments, and indicate potential results where applicable, to investigate the following.

(a) Changes in proliferative index when treated with the aptamers

(b) Changes in mRNA expression of target genes for EGFR

(c)   Changes in the phosphoprotein content of cells

Expert's answer

1) Aptamers bind to cells expressing EGFR , they block receptors autophosphorylation and prevent proliferation of tumour cells . Hence there is a change in proliferative index. Ligand binding and dimerization causes autophosphorylation of the intracytoplasmic domain and activation of the intracellular tyrosine kinase pathway, there by causing proliferation.

2) genetic studies have demonstrated that the EGFR gene aberration is the most frequent predominant event in high grade gliomas, and is associated with high levels of Egfr mRNA or protein expression.

Antisense approach targeting Egfr could inhibit significantly not only the Egfr expression but also the cell proliferation of malignant glioma .

Null mutations in glial cells leading to production of nonfunctional EGFR.

3) when EGFR binding to its ligand results in auto phosphorylation by intrinsic tyrosine/kinase activity leading to cell proliferation. When aptamer bind to EGFR it does not allow EGFR to bind. So changes occur in phosphoprotien content of EGFR cells.

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