The transcriptional program regulated by the tumor suppressor
p53 was analysed using oligonucleotide microarrays. A human lung
cancer cell line that expresses the temperature sensitive murine
p53 was utilized to quantitate mRNA levels of various genes at
different time points after shifting the temperature to 32 degrees
C. Inhibition of protein synthesis by cycloheximide (CHX) was
used to distinguish between primary and secondary target genes
regulated by p53. In the absence of CHX, 259 and 125 genes were
up or down-regulated respectively; only 38 and 24 of these genes
were up and down-regulated by p53 also in the presence of CHX
and are considered primary targets in this cell line. Cluster
analysis of these data using the super paramagnetic clustering
(SPC) algorithm demonstrate that the primary genes can be distinguished
as a single cluster among a large pool of p53 regulated genes.
This procedure identified additional genes that co-cluster with
the primary targets and can also be classified as such genes.
In addition to cell cycle (e.g. p21, TGF-beta, Cyclin E) and apoptosis
(e.g. Fas, Bak, IAP) related genes, the primary targets of p53
include genes involved in many aspects of cell function, including
cell adhesion (e.g. Thymosin, Smoothelin), signaling (e.g. H-Ras,
Diacylglycerol kinase), transcription (e.g. ATF3, LISCH7), neuronal
growth (e.g. Ninjurin, NSCL2) and DNA repair (e.g. BTG2, DDB2).
The results suggest that p53 activates concerted opposing signals
and exerts its effect through a diverse network of transcriptional
changes that collectively alter the cell phenotype in response
to stress.