L1CAM and breast carcinoma: 2A). MDA-MB-468 cell lysates showed a very low level of L1 protein expression overall. This suggested that our breast cancer cells proteolyzed L1CAM via ADAM10 to release the large ectodomain fragment. We then checked for the presence of soluble L1 in cell culture medium by TCA precipitation. Phorbol ester (PMA) stimulation was reported to increase L1 shedding by ADAM10 [9,30]. As seen in Figure 2B, PMA treatment resulted in a significant increase of soluble L1 (sL1) at 180 kDa in the culture medium compared to samples prior to treatment.