mitogens

A Mitogen, or somatomedin, is any molecules that stimulates a cell to divide.

Most mitogens are proteins, and they stimulate signal transduction pathways that utilize mitogen activated protein kinases. Mitogens include cytokines, growth factors, hormones, neurotransmitters, cellular stress proteins, and cell adhesion ligands. For example, antigen stimulation of cell adhesion immunoglobulins triggers mitosis in B cells.

Mitogen activated protein kinases (MAP kinases) act as switch kinases that transmits information of increased intracellular tyrosine phosphorylation to that of serine/threonine phosporylation. MAPK-activated protein kinases (or MKs; formerly MAPKAP kinases) respond to mitogenic and stress stimuli through proline-directed phosphorylation and activation of the kinase domain by extracellular signal-regulated kinases 1 and 2 and p38 MAPKs.(ffta)

The signaling cascade is:
mitogen → MAPKK kinase (MAPKKK) → MAPK kinase (MAPKK) → MAP kinase (MAPK) → signaling

Among the substrates of ERK are the members of the p90 ribosomal S6 kinase (RSK) family of serine/threonine kinases (10). RSK plays an active role in nuclear signaling by phosphorylating the cyclic AMP response element binding protein (CRE-binding protein, CREB) (33), c-Fos (5), and IB (27). Phosphorylation of Bad (3, 29) and C/EBPß (4) by RSK can protect cells from apoptosis. RSK has also been implicated in cell cycle regulation. RSK phosphorylates histone H3 (25), suggesting that RSK may regulate chromatin remodeling.[s-fft]

MAP kinases are also called ERKs for extracellular-signal regulated kinases, microtubule associated protein-2 kinase (MAP-2 kinase), myelin basic protein kinase (MBP kinase), ribosomal S6 protein kinase (RSK-kinase) and EGF receptor threonine kinase (ERT kinase). Maximal MAP kinase activity requires phosphorylation of both tyrosine and threonine residues. Activators of the extracellular-signal regulated kinase family (ERKs) of MAPKs include the mitogens, Ras [fft], polypeptide growth factors PDGF, CSF-1, IGF-1, EGF insulin, PMA.

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basophils

Basophils are granulocytes packed with granules that stain basic (purple with H&E).

The nucleus is bilobed, and the metachromatic granules contain sulfated glycosaminoglycans as well as vasoactive compounds – histamine and proteoglycans. Lysosomal arylsulfatase is found in granules of developing basophils in bone marrow.

Basophil granules are surrounded by a unit membrane and contain particles which are uniform in size across the same granule yet vary in size in different granules within the same cell. Some granules reveal a homogeneous texture and/or "myelin" figures. [s] Though basophils and mast cells share morphological features, the appearance of most basophil granules differs from the ultrastructure of human mast cell granules.

Activated basophils release proinflammatory histamine and proteoglycans from granules, and synthesize then secrete leukotrienes and cytokines (particularly IL-4). Histamine and IL-4, which is associated with production of IgE, are involved in allergic reactions.

Basophils are the least common granulocyte, representing about 0.5% to 1% of circulating leukocytes. A low basophil count combined with a low neutrophil count almost always portends leukemia.

Tables  Fc receptors  Immune Cytokines  Immunoglobulins .

tags [Immunology][leukocytes]