Enhanced cell cycle progression and down regulation of p21(Cip1/Waf1) by PRL tyrosine phosphatases

Human PRL-1, PRL-2, and PRL-3 tyrosine phosphatases induce the malignant transformation of epithelial cells. We tested the hypothesis that the oncogenic effects of PRL occur by increasing cellular proliferation. Cells stably transfected with PRL-1 or PRL-2 exhibited 2.7-3.3-fold increases over control cells in the rate of DNA synthesis and the proportion of cells in S-phase, and they progressed more rapidly from G1 into S. In addition, cells overexpressing either PRL-1 or PRL-2 exhibited enhanced cyclin-dependent kinase 2 (CDK2) activity and significantly lower p21(Cip1/Waf1) protein levels, and PRL-1 overexpressing cells had higher cyclin A protein levels than control cells. We conclude that PRL phosphatases increase cell proliferation by stimulating progression from G1 into S phase, and this process may be dependent on the down regulation of the cyclin dependent kinase inhibitor p21(Cip1/Waf1).     

Elevated levels of prostate-specific antigen (PSA) in prostate cancer cells expressing mutant p53 is associated with tumor metastasis

The underlying basis for rising levels of prostate-specific antigen (PSA) in prostate cancer is not fully understood, but attention has turned to the possibility that loss of normal p53 function might be directly involved. We have investigated the relationship between p53 function and PSA expression using in vitro and in vivo approaches. Three prostate cancer-derived p53 mutants (F134L, M237L, R273H) were introduced into LNCaP prostate cancer cells and stable transfectants established. Expression of mutant p53 was demonstrated by Western blot analysis, inactivation of wtp53 function, and a loss of p53-dependent responses to DNA damage induced by UV-irradiation and cisplatin. Levels of PSA mRNA and secreted protein were determined by RT-PCR and Western blotting, respectively. Serine protease activity was assessed using an esterase assay. In vivo effects of mutant p53 expression were examined after orthotopic implantation into prostates of nude mice. Expression of all p53 mutants was associated with elevated PSA mRNA and secreted PSA protein. In a representative line, mutant p53 was also associated with increased PSA protease-like activity compared with a control line expressing wildtype p53. Overall PSA levels, and PSA levels in serum from mice bearing tumors derived from cells expressing mutant p53, were increased compared with levels in mice bearing tumors derived from control cells. In addition, the tumors derived from cells with mutant p53 had increased vascularization and induced lymph node metastases. These data provide in vitro and in vivo support for the notion that p53 mutations directly contribute to increased levels of serum PSA, and are associated with more aggressive tumors.     

Loss of heterozygosity in serial plasma DNA samples during follow-up of women with breast cancer

We evaluated the potential utility of occult circulating tumor DNA as a molecular marker of disease in subjects previously diagnosed with breast cancer. Using 24 microsatellite markers located at sites of frequent loss of heterozygosity (LOH) or allele imbalance in breast cancer, we analyzed DNA from 16 primary tumors (Stage IIA or more advanced) and 30 longitudinally collected plasma specimens. Clinical data at the time of plasma collection were obtained. All 16 tumors were characterized by an individual pattern of LOH. LOH was detected in 12 of 30 (40%) plasma samples, taken from 8 of 14 (57%) subjects. However, the number of LOH in plasma was small (n = 15), and the mean proportion of LOH was much lower than in the tumors (0.05 vs. 0.52). Although infrequent, 12 of 15 (80%) plasma LOH were concordant with abnormalities in the paired tumors, and the mean percent LOH was higher than in normal plasmas, suggesting that they were authentic tumor-derived abnormalities. We found, despite this, no association, between plasma LOH and tumor stage or clinical status at time of blood collection (i.e., LOH was as common in subjects with no evident disease as in those with evident disease). In addition, detection of LOH was not consistent between serial samples from 5 of 11 subjects (45%), despite stable clinical conditions. No association with clinical outcome was evident, although the sample size was small. Microsatellite instability in plasma was infrequent, nonconcordant with paired tumor and inconsistent in serial samples. This pilot study suggests that identifying tumor-specific LOH in the plasma of breast cancer subjects may not be useful for detecting occult metastases or for monitoring disease. Other detection techniques may be more promising, but circulating tumor DNA may not be a sufficiently accurate reflection of breast cancer clinical status or tumor activity.     

Recent trends and racial/ethnic differences in the incidence and treatment of ductal carcinoma in situ of the breast in California women

BACKGROUND: The rapid increase in the incidence of ductal carcinoma in situ (DCIS) of the breast in the U.S. has been associated with the widespread adoption of screening mammography. Little is known regarding the incidence and treatment of DCIS in women of racial/ethnic groups other than white and black. The current investigation examined recent trends and racial/ethnic differences in the incidence and treatment of DCIS in California. METHODS: All cases of DCIS diagnosed in women age > or = 40 years in California between 1988-1999 were included. Age-adjusted incidence rates for white, black, Hispanic, and Asian-Pacific Islander women were calculated using the 2000 U.S. female population as the standard. The estimated annual percent change (EAPC) in the rates was calculated using least squares regression. RESULTS: The average annual age-adjusted incidence of DCIS (1988-1999) was 45.3 per 100,000 in white women, 35.0 in black women, 30.9 in Asian-Pacific Islander women, and 21.8 in Hispanic women. Although a steady increase in the incidence of DCIS was noted in all racial/ethnic groups over the study period, Asian-Pacific Islander women were found to have experienced the steepest increase (EAPC = 9.1%), particularly in the age group 50-64 years (EAPC = 12.0%). The DCIS incidence was reported to increase with age in white, black, and Hispanic women, but remained fairly constant after the age of 50 years in Asian-Pacific Islanders. The proportion of women with DCIS treated with mastectomy decreased from 53% in 1988 to 32% in 1999. Younger women and Asian-Pacific Islander women reportedly were more likely to undergo mastectomy. CONCLUSIONS: Considerable differences by race/ethnicity and age were observed in DCIS incidence and the change in the incidence in California between 1988 and 1999. Further information is needed to determine whether these differences are because of differential utilization of screening mammography or biologic characteristics of DCIS lesions.     

Shc proteins are strong, independent prognostic markers for both node-negative and node-positive primary breast cancer

Activated Shc signaling proteins are implicated in many pathways associated with aggressive disease, and many breast cancer cell lines derived from highly aggressive tumors contain high levels of activated, tyrosine phosphorylated (PY)-Shc (the M(r) 46000 and M(r) 52000 isoforms) relative to levels of an inhibitory M(r) 66000 Shc isoform. It was, therefore, hypothesized that high amounts of PY-Shc relative to the M(r) 66000 Shc isoform would serve as a marker for aggressive neoplasms. Semiquantitative immunohistochemical analyses of PY-Shc and p66 Shc were performed on archival primary breast tumor specimens from 116 women, 17 of whom experienced relapse (6.1 years median follow-up of nonrelapsed patients). Consistent with our hypothesis, staining intensities demonstrated that increased amounts of PY-Shc (P = 0.01) and decreased expression of p66-Shc protein (P = 0.028) correlated with disease recurrence. Modeled as the ratio of PY-Shc to p66 Shc, the Shc ratio correlated strongly with nodal status (P = 0.003), tumor stage (P = 0.0025), and disease stage (P = 0.002) and was 2-fold higher in primary tumors of patients who subsequently relapsed (P < 0.001). Univariate Cox proportional hazards analysis of relapse-free survival demonstrated the prognostic value of PY-Shc (P = 0.01), p66 Shc (P = 0.04), and the Shc ratio (P = 0.004) as continuous variables, with a hazard ratio (HR) of 10 (P = 0.007) for the Shc ratio. Shc ratio cut points of <0.35 and >0.65 were identified and independently validated to maximize negative predictive value and positive predictive value. Patients with low Shc ratios (n = 36) had a 0.08 HR of relapse (P = 0.007) compared with patients with high Shc ratios, experiencing an 8-year cumulative 2.9% and 55% relapse hazard, respectively, compared with a 22% relapse hazard in the total cohort. The Shc ratio had similar prognostic value for disease-specific survival. In multivariate models, the Shc ratio, both as a continuous variable and as a cut point-categorized variable, was independent of all measured covariates (including nodal status, tumor stage, disease stage, grade, estrogen receptor status, and adjuvant therapy) and was a stronger prognostic marker than all but nodal status. All relapsed node-positive patients had very high Shc ratios (>0.80; P = 0.006) in their primary tumors. Furthermore, the Shc ratio was a strong, independent prognostic indicator in node-negative patients (79 patients, 10 recurrences), with a HR of 0.086 (P = 0.02) that was independent of clinical markers and adjuvant therapy. Patients with low and high Shc ratios experienced a 3.6% and 64% relapse hazard, respectively, compared with 20% in the total node-negative cohort.