Trophoendodermal stem cell-derived extracellular matrices: absence of detectable entactin and presence of multiple laminin species.

Extracellular matrices (ECM) generated by trophoendodermal stem cells transplanted into the peritoneum of host rats were investigated. Two types of trophoendodermal transplants were studied: (1) free-floating cystic structures, and (2) solid masses adherent to various abdominal organs. Trophoendodermal stem cell ECM obtained from either transplant source was dominated by the presence of laminin similar to Engelbreth-Holm-Swarm (EHS) tumour ECM. However, in contrast to EHS tumour ECM, another ECM component, entactin, was below the level of detection in trophoendodermal stem cell ECM. The laminins present in the two types of trophoendodermal stem cell transplants exhibited distinct differences. Tissues used as sources of one type of laminin were devoid of the other type of laminin. The two species of rat laminin behaved similarly on sodium dodecyl sulphate-polyacrylamide gels and had virtually identical amino acid compositions. The laminins also had similar cruciform patterns when examined by rotary shadowing. Rat laminins differed in their binding to an ion exchange resin: laminin isolated from peritoneal cysts bound to the resin (acidic laminin); laminin isolated from solid masses failed to bind (basic laminin). Acidic rat laminin showed reduced capacity to form laminin-laminin associations when compared with basic rat laminin. Acidic/soluble laminin proved to be a useful reagent in the development of a radio-immunoassay for laminin. Laminin concentrations in the peritoneal fluid of transplant-bearing rats was very high (approximately 400 micrograms/ml) and entirely of the acidic/soluble form. In summary, trophoendodermal stem cell ECM possesses a distinct composition with a lack of detectable entactin, and trophoendodermal stem cells are capable of modulating the characteristics of laminin, depending upon their organization. These features of trophoendodermal stem cell ECM may represent signals responsible for at least some of the unique features of the trophoendodermal stem cell transplants.