VEGFA Notes - ISOFORMS Project

Key Isoform Biology

VEGFA has 17 named isoforms from alternative splicing, representing extreme diversity in isoform function.

Major Isoforms by Length

Isoform	UniProt ID	Length	Heparin Binding	Matrix Bound	Key Feature
VEGF206	P15692-1	206 AA	Strong	Yes	Longest, matrix-bound
VEGF189	P15692-2	189 AA	Strong	Yes	Matrix-bound
VEGF165	P15692-4	165 AA	Moderate	Intermediate	Canonical "VEGF"
VEGF121	P15692-9	121 AA	None	No	Freely diffusible
VEGF165B	P15692-8	165 AA	?	?	ANTI-ANGIOGENIC

Critical Isoform Difference: VEGF165 vs VEGF165B

UniProt explicitly states for VEGF165B:

"Binds to the KDR receptor but does not activate downstream signaling pathways, does not activate angiogenesis and inhibits tumor growth" PMID:15520188

This means:
- VEGF165: Pro-angiogenic, promotes tumor growth
- VEGF165B: Anti-angiogenic, inhibits tumor growth

Same length (165 AA), same receptor binding, but opposite biological effects!

Heparin Binding and Matrix Association

The longer isoforms (VEGF189, VEGF206) contain heparin-binding domains and remain matrix-bound, creating:
- Steep gradients - important for vessel sprouting
- Localized signaling - concentrated at source

The shorter isoform (VEGF121) lacks heparin binding:
- Freely diffusible - spreads through tissue
- Broad signaling - less directional

GOA Annotation Status

267 total annotations
NO isoform-specific annotations (no P15692-X identifiers)
Likely conflates pro-angiogenic (most isoforms) with anti-angiogenic (VEGF165B) functions

Expected Annotation Issues

Angiogenesis annotations - should specify which isoforms
"Positive regulation of angiogenesis" - NOT true for VEGF165B
VEGFR binding - all isoforms bind, but different downstream effects

Key References

PMID:15520188 - VEGF165B anti-angiogenic properties
Original VEGF papers describing isoform differences