Essential Cell Biology 5th edition

Essential Concepts
729
Figure 20–53 Anti-immune-checkpoint antibodies release a killer
cell attack on cancer cells. The antibodies disinhibit the killer cells
that recognize the novel parts of the proteins encoded by the mutant
oncogenes of the cancer cells. A patient with advanced metastatic
melanoma received treatment with such an antibody called ipilimumab.
After 16 weeks of treatment, the tumors were noticeably smaller, and by
week 72 they had essentially been eliminated. (From A. Hoos et al.,
J. Natl Cancer Inst. 102:1388−1397, 2010.)
week 12
chronic myeloid leukemia (CML), the misbehavior of the cancer cells
depends on a mutant intracellular signaling protein (a tyrosine kinase)
that causes the cells to proliferate and survive when they should not.
A small drug molecule, called imatinib (trade name Gleevec), blocks
the activity of this hyperactive mutant kinase. The results have been a
dramatic success: in many patients, the abnormal proliferation and survival
of the leukemic cells are strongly inhibited, providing many years of
symptom-free patient survival. The same drug is also effective in some
other cancers that depend on similar oncogenes.
With these examples before us, we can hope that our modern understanding
of the molecular biology of cancer will soon allow us to devise
effective rational treatments for even more forms of cancer. At the same
time, cancer research has taught us many important lessons about basic
cell biology. The applications of that knowledge go far beyond the treatment
of cancer, giving us insight into the way that cells and organisms
develop and operate.
week 16
week 72
ESSENTIAL CONCEPTS
• Tissues are composed of cells and extracellular matrix.
• In plants, each cell surrounds itself with extracellular matrix in the
form of a cell wall, which is made chiefly of cellulose and other
polysaccharides.
• An osmotic swelling pressure on plant cell walls keeps plant tissue
turgid.
• Cellulose microfibrils in the plant cell wall confer tensile strength,
while other cell-wall polysaccharides resist compression.
• The orientation in which the cellulose microfibrils are deposited in
the cell wall controls the orientation of plant cell growth.
• Animal connective tissues provide mechanical support to organs and
limbs; these tissues consist mainly of extracellular matrix, which is
secreted by a sparse scattering of embedded cells.
• In the extracellular matrix of animals, tensile strength is provided
by the fibrous collagen proteins, while glycosaminoglycans (GAGs),
covalently linked to proteins to form proteoglycans, act as spacefillers
and provide resistance to compression.
• Transmembrane integrin proteins link extracellular matrix proteins
such as collagen and fibronectin to the intracellular cytoskeleton of
cells that contact the matrix.
• Cells are connected to one another via cell junctions in epithelial
sheets that line all external and internal surfaces of the animal body.
• Cell adhesion proteins of the cadherin family span the epithelial cell
plasma membrane and bind to identical cadherins in adjacent epithelial
cells.
• At an adherens junction, the cadherins are linked to intracellular
actin filaments; at a desmosome junction, they are linked to intracellular
keratin intermediate filaments.
ECB5 n20.103-20.57