Biomedical Engineering Reference
In-Depth Information
Definition of Terms
Atypical protein kinase C:
One of the three subfamilies of the protein kinase C. h issubfamily
is characterized by the requirements for activation. As opposed to the other subfamilies
(conventional PKCs, novel PKCs), the atypical PKCs do not require diacylglycerol
(DAG) or Ca
2+
ions for activation, and they are not activated by phorbol esters.
Cell adhesion molecules:
Integral membrane proteins that mediate the interaction between
cells. h ey can bind homophilically to the same molecule or heterophilically to a dif erent
molecule on the adjacent cells. h e most prominent families of adhesion molecules are
cadherins, immunoglobulin-superfamily adhesion molecules and integrins.
Cell polarity:
h e asymmetric distribution of organelles or proteins in the cells.
Inl ammation:
A process characterized by massive ini ltration of leukocytes to sites of antigen
deposition. Under normal circumstances, inl ammation serves antigen clearance and is
tightly regulated. When misregulated, it can lead to tissue damage.
Membrane polarity:
Refers to dif erent membrane identities regarding their composition of
lipids and proteins. In epithelial and endothelial cells, the apical membrane (facing the
lumen of an organ) and the basolateral domain (in contact with neighboring cells and
the extracellular matrix) dif er in their composition. Membrane polarity is important for
the specii c uptake and the vectorial transport of molecules.
Par proteins:
A family of proteins originally discovered in
C. elegans
as regulators of the
asymmetric distribution of cytoplasmic granules in the fertilized egg. h ese proteins
turned out to be master regulators of cell polarity in many dif erent organisms and cell
types.
Sertoli cell:
A cell type within the male reproductive tract. Undergoes homotypic cell-cell
interactions to form the blood-testis barrier to prevent the interaction of blood-borne
molecules or cell types with developing germ cells. Undergoes heterotypic interactions
with developing sperm cells to provide nutrients and development signals.
Small GTPase:
Protein that binds guanine nucleotides and shuttles between an inactive state
(GDP bound) and an active state (GTP bound). Contains intrinsic activity to hydrolyze
bound GTP to GDP. GTP hydrolysis deactivates the GTPase.
Stem cell:
A cell type with the ability to renew itself and to give rise to dif erent daughter
cells by a process called asymmetric cell division. Hematopoietic stem cells give rise to
all cells of the immune system.
Tight junctions:
A structure at the cell-cell contacts between epithelial or endothelial cells
that appears as discrete spots of membrane fusions by electron microscopy. h e tight
junctions regulate paracellular dif usion of molecules as well as lumen formation and
prevent the intermixing of distinct membrane domains.
References
Adams, C.L. and Y.T. Chen, S.J. Smith, and W.J. Nelson. 1998. Mechanisms of epithelial cell-
cell adhesion and cell compaction revealed by high-resolution tracking of E-cadherin-
green l uorescent protein. J. Cell. Biol. 142: 1105-1119.
Aurrand-Lions, M. and C. Lamagna, J.P. Dangeri eld, S. Wang, P. Herrera, S. Nourshargh,
and B.A. Imhof. 2005. Junctional adhesion molecule-C regulates the early inl ux of
leukocytes into tissues during inl ammation. J. Immunol. 174: 6406-6415.
