The term<unk>  refers to a naturally occurring protein capable of stimulating cellular proliferation and cellular differentiation.<unk> s are important for regulating a variety of cellular processes.<unk> s typically act as signaling molecules between cells. Examples are cytokines and hormones that bind to specific receptors on the surface of their target cells.
They often promote cell differentiation and maturation, which varies between<unk> s. For example, bone morphogenic proteins stimulate bone cell differentiation, while vascular endothelial<unk> s stimulate blood vessel differentiation.
Growth factor
Gasotransmitter
Receptor 
Tumor antigen
Thromboxane
Prostaglandin
Steroid hormone
Glycoprotein