We have previously reported that loss of p53 tumor suppressor protein results in centrosome hyperampli®ca-tion, which leads to aberrant mitosis and chromosome instability. Since p53 is either deleted or mutated in human cancers at a high frequency, we investigated whether human cancers showed centrosome hyperampli®cation. Screening of advanced stage breast ductal carcinomas and squamous cell carcinomas of the head and neck (SCCHN) revealed that centrosome hyperampli®cation is frequent in both tumor types. Moreover, through the analyses of p53 in SCCHN samples by direct sequencing and by loss-of-heterozygosity test, we found that p53 mutations correlated with occurrence of centrosome hyperampli®cation. However, in some cases, we observed centrosome hyperampli®cation in tumors that retained wild-type p53. These tumors contained high levels of Mdm2. Since Mdm2 can inactivate p53 through physical association, we investigated whether Mdm2 overexpression induced centrosome hyperampli®cation. We found that Mdm2 overexpression, like loss of p53, induced centrosome hyperampli®cation and chromosome instability in cultured cells.
Astrocyte proliferation is tightly controlled during development and in the adult nervous system. In the present study, we find that a high-molecular-weight (MW) form of the glycosaminoglycan hyaluronan (HA) is found in rat spinal cord tissue and becomes degraded soon after traumatic spinal cord injury. Newly synthesized HA accumulates in injured spinal cord as gliosis proceeds, such that high-MW HA becomes overabundant in the extracellular matrix surrounding glial scars after 1 month. Injection of hyaluronidase, which degrades HA, into normal spinal cord tissue results in increased numbers of glial fibrillary acidic protein (GFAP)-positive cells that also express the nuclear proliferation marker Ki-67, suggesting that HA degradation promotes astrocyte proliferation. In agreement with this observation, adding high- but not low-MW HA to proliferating astrocytes in vitro inhibits cell growth, while treating confluent, quiescent astrocyte cultures with hyaluronidase induces astrocyte proliferation. Collectively, these data indicate that high-MW HA maintains astrocytes in a state of quiescence, and that degradation of HA following CNS injury relieves growth inhibition, resulting in increased astrocyte proliferation.
Inactivation of tumor suppressor genes, including p53 and retinoblastoma (Rb), are commonly found in all cancers, including head and neck squamous cell carcinoma. Alterations at either p53 or Rb, however, are only weakly associated with tumor aggressiveness. In many cancers loss of heterozygosity (LOH) at multiple loci is associated with decreased survival. The polymerase chain reaction and highly informative microsatellite markers were used to compare DNA from matched sets of 63 head and neck squamous cell cancers and normal tissue for LOH at the p53 and Rb loci. At p53, 50 were informative, with LOH occurring in 19 (38%). Of the 57 that were informative at Rb, LOH occurred in 21 (37%). Of the 46 that were informative at both p53 and Rb, LOH occurred in 10 (22%) at both loci. When LOH for p53 and Rb individually was compared to stage, differentiation, and survival, there was no correlation. However, the patients with LOH at both loci had a significantly poorer survival (P = .009). This strongly supports the contention that simultaneous alterations of these two tumor suppressor genes favor tumor aggressiveness and can be used as a prognostic indicator.
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