Question

heregulin (hrg) is a ligand that can bind to either her3 or her4 and is implicated in a number of cancers. a fret is observed between cfp-grb2 and yfp-sos if hrg is added to normal her4 cells. in contrast no fret is observed between cfp-grb2 and yfp-sos if hrg is added to normal her3 cells, but is observed if her3 expressing cells also have amplified her2 genes. what do these observations indicate about her3 and her4

Answer 1

HER3 alone does not lead to FRET, but when HER2 is present in excess, HRG can activate the downstream signaling pathway.

Step-by-step explanation:

The observations indicate that HER3 and HER4 are different receptor proteins that can interact with heregulin (HRG). When HRG is added to normal HER4 cells, a FRET (Fluorescence Resonance Energy Transfer) is observed between CFP-GRB2 and YFP-SOS.

This suggests that the binding of HRG to HER4 activates the downstream signaling pathway involving GRB2 and SOS. On the other hand, no FRET is observed between CFP-GRB2 and YFP-SOS when HRG is added to normal HER3 cells.

However, when HER3-expressing cells also have amplified HER2 genes, FRET is observed. This indicates that HER3 alone is not sufficient for FRET, but when HER2 is present in excess, it allows HRG to activate the downstream signaling pathway.