LPA and S1P regulate tumor cell invasion of 3D collagen matrices. (A) HT1080, A2058, SKOV3 or HEK293 cells were induced to invade 3D collagen gels (3.75 mg/ml or 2.0 mg/ml) under serum-free conditions in the presence or absence of LPA alone (1 μM), S1P alone (1 μM), or both LPA and S1P (1 μM each). After 48 hours, cultures were fixed, stained, and images were acquired to demonstrate the effects of LPA and S1P on tumor cell invasion. Arrowheads indicate the position of the tumor cell monolayer at the initiation of invasion. Magnification = 20×. Scale bar = 50 μm. Inset (panel A) = higher power magnification of invading HT1080 cell. (B) Quantitation of tumor invasion from panel A. Data are expressed as mean numbers of invading cells per HPF (20×) (± S.D.) from a minimum of 20 fields.