Sarcolectin is an endolectin present in a great variety of conjunctival tissues (muscles, cartilage,
sarcomas), but also in brain or
placental extracts of vertebrates, including primates. When purified to electrophoretical homogeneity as a 65-kd
protein, it agglutinates cells and has an affinity for
simple sugars. In addition, it is able to inhibit the synthesis of
interferon (IFN)-dependent secondary
proteins and to restore cells to their status ad primum. The
biological effect of
Poly(I).
Poly(C)-induced feedback
interferon is inhibited by the addition of sarcolectins, which also abolishes cellular refractoriness to repeated IFN induction. Similarly, sequential association of, first,
Poly(I).
Poly(C); 4-5 h later,
sarcolectin restores the full capacity of both to promote cell growth, unrestrained by IFN. Indeed, the secondary
proteins which are in the process of being synthesized are inhibited. In a great variety of animal cells,
sarcolectin can also initiate growth after it has been blocked by IFN. This is not an all-or-none effect, but a balance may be struck by IFN and
sarcolectin, depending on their respective concentrations and specific activity. We propose that the coordination of these cellular functions of
Poly(I).
Poly(C), IFN, and
sarcolectin takes place in the form of a triangular growth-regulatory cycle and postulate that they thus maintain a balance during differentiated normal tissue development.