The presence of 19-kDa Bcl-2 in dividing cells

The 26-kDa bcl-2 gene product inhibits apoptosis and cell proliferation. Cleavage of Bcl-2 into a 22-kDa fragment inactivates its anti-apoptotic activity and is a key event in apoptosis. Here, and in recent work, we describe massive 19-kDa Bcl-2 immunoreactivity in non-apoptotic cells, suggesting a link with viability rather than cell death. Loss of 19 kDa Bcl-2 in adriamycin-induced apoptotic cells underlines this. G2/M-phase accumulation of cells by nocodazole-treatment also results in loss of 19 kDa Bcl-2. Next to its well-documented cytoplasmic localization, a substantial pool of Bcl-2 resides in nuclei. Hampered nuclear localization of Bcl-2 leads to a loss of cell cycle repression. This has led us to point at a pivotal role for nuclear Bcl-2 in cellular proliferation. In this report, cellular fractionation of bcl-2 transfected cells in various phases of the cell cycle reveals a constitutive cytoplasmic pool of 19 kDa Bcl-2. Nuclear 19-kDa Bcl-2 immunoreactivity is far more pronounced in rapidly dividing nuclei compared with more quiescent nuclear fractions. This implicates that ongoing cell proliferation involves cleavage of nuclear Bcl-2 with a 19-kDa fragment.

The role of various Bcl-2 domains in the anti-proliferative effect and modulation of cellular glutathione levels: a prominent role for the BH4 domain

Reduced cell proliferation and increased levels of cellular glutathione (GSH) are characteristic for cells that overexpress the anti-apoptotic Bcl-2 protein. We investigated the influence of various Bcl-2 domains on both these characteristics. Rat CC531 colorectal cancer cells were stably transfected with the human bcl-2 gene (CCbcl2 cells) or with bcl-2 gene constructs missing a coding sequence for a func-tional domain, BH1 (CCDeltaBH1 cells), BH3 (CCDeltaBH3 cells), BH4 (CCDeltaBH4 cells) or the transmembrane region (CCDeltaTM cells). We measured GSH levels in exponentially and confluent growing bcl-2-transfected cell populations. The fraction of S-phase cells during exponential growth was significantly reduced in CCbcl2, CCDeltaBH1, CCDeltaBH3, and CCDeltaTM cells compared with parental CC531, neo-transfected CC531 and CCDeltaBH4 cells. GSH levels in these bcl-2 transfectants were significantly higher than in the parental line measured at 50% confluence; at 100% confluence they reached a similar level as found in parental cells. Independently from the presence of BH1, BH3 or TM domains, overexpression of Bcl-2 reduces cellular proliferation under conditions of increased GSH levels. This apparent link is lost in CCDeltaBH4 cells; these cells are not reduced in cellular proliferation and harbour significantly higher GSH levels than found in the other transfectants. Studies on the subcellular localization revealed an extremely low expression of the Bcl-2 protein lacking the N-terminal BH4 domain in nuclear fractions. Nuclear translocation of Bcl-2 requires the presence of the BH4 domain and seems prominent in reducing cellular proliferation.

Delivery of anticancer drugs via isolated hepatic perfusion: a promising strategy in the treatment of irresectable liver metastases?

The prognosis of patients with irresectable liver metastases derived from colorectal cancer is invariably poor; unfortunately, these tumours show only minor responses to conventional anticancer agents. The best responses have been obtained by fluoropyrimidines delivered as continuous infusion into the hepatic artery (HAI): their rapid uptake and detoxification by liver cells results in relatively low systemic drugs levels. This approach increases mean survival duration from 17 to 26 months and, in few patients, causes "down-staging" that may result in resectability. To improve opportunities for chemotherapy, the technique of 1-hour recirculating perfusion of the vascularly isolated liver (isolated hepatic perfusion, IHP) was developed. If leakage to the systemic circulation is negligible-and the compounds used do not readily cause hepatotoxicity-IHP allows usage of drug doses that would be fatal if delivered systemically. Because alkylating agents generally have steep dose-response curves, mitomycin C (MMC) and melphalan (L-PAM) entered phase I/II studies on IHP. Using these drugs, IHP was performed in principle as a single procedure in 60 otherwise untreated patients at our institution. However, despite preliminary data that indicate impressive clinical responses are obtained, improvement over HAI will probably be minor. Because IHP is a complicated way of drug delivery, one could argue that its use is justified only when it has the potential to kill all tumour cells in the liver. We critically discuss the possibilities of IHP and/or the use of gene therapy in an IHP setting.

Microwave-enhanced in situ end-labeling of fragmented DNA: parametric studies in relation to postmortem delay and fixation of rat and human brain

In situ end-labeling (ISEL) identifies DNA fragmentation in apoptotic or necrotic nuclei in tissue sections. However, application of ISEL on human brain requires conservation of DNA integrity during the postmortem delay (PMD) and good accessibility of fragmented DNA after (prolonged) tissue fixation. We therefore investigated ISEL in relation to PMD and fixation in rat and human brain. Application on a unilateral lesion model in perfused rat brain revealed that prolonged post-fixation strongly diminished ISEL results. However, microwave pre-treatment can counteract these masking effects without inducing nonspecific labeling contralaterally. On the other hand, in briefly post-fixed, perfused brain or immersion-fixed rat and human PMD brain, microwave pre-treatment was deleterious and induced strong nonspecific labeling. In young rat brain, PMD did not influence the low numbers of apoptotic nuclei until 24 hr PMD, when massive nuclear labeling occurred. In human cortex, DNA fragmentation patterns were independent of duration of fixation or PMD and were already present from 4.25 hr PMD onwards. Our data suggest that ISEL on human brain represents antemortem DNA damage rather than PMD artifacts. Furthermore, microwave pre-treatment appears beneficial only in particular fixation conditions.

Immunoreactivity of proliferating cell nuclear antigen compared with bromodeoxyuridine incorporation in normal and neoplastic rat tissue

Monoclonal antibodies (MoAbs) against proliferating cell nuclear antigen (PCNA) represent a potentially useful tool for cell kinetic analysis of tumours. Because in paraffin-embedded tissue the relationship between PCNA immunoreactivity and tumour cell proliferation is not well characterized, we have compared PCNA positivity as detected by the PC10 MoAb with the bromodeoxyuridine labelling index (BrdUrd-LI) in two different transplantable hormone-dependent rat mammary tumours. Together, these two tumour models (MCR-83 and EMR-86) cover a wide range of S-phase fractions. Evaluating 31 methacarn-fixed tumours, a strong but non-linear relationship (r = 0.98) was obtained. PCNA-positive fractions were invariably higher than corresponding BrdUrd-LIs and also higher than the estimated growth faction: growth fractions as determined by continuous BrdUrd labelling of the tumour and stromal cell population in EMR-86 carcinomas were 12 and 26 per cent lower than PCNA-positive fractions, implying that a certain fraction of non-cycling cells can also express PCNA. A dramatic disturbance in the relationship of PCNA positivity and the BrdUrd-LI was observed in the EMR-86 model after growth arrest induced by hormonal ablation: PCNA immunoreactivity remained detectable for at least 3 days, whereas the BrdUrd-LI decreased almost immediately. In comparison, PCNA immunoreactivity persisted for a much shorter period in small intestinal cells that had stopped DNA replication when moving from the crypt towards the villus. It is concluded that although differences in PCNA expression exist between various tissues, PCNA as detected by the PC10 MoAb may be used in tumours as an operational marker for the growth fraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Surgically induced cytokinetic responses in experimental rat mammary tumor models

The effect of surgical removal of "primary" tumors on the cytokinetics of local tumor remnants, secondary implants, and metastases was investigated in three different rat tumor models in the Wag/Rij rat: a slow-growing (MCR83) and a fast-growing (EMR86) hormone-dependent mammary tumor and a rapidly, but autonomously growing carcinoma (MCR86). The latter two tumors had metastatic potential. Cell kinetic studies were done using in vivo labeling with 5'-bromodeoxyuridine (BrdUrd). Thirty-three hours after removal of a subcutaneous MCR83 flank tumor, secondary implants showed a significant (P less than 0.05) but transient increase in the BrdUrd labeling index (LI). A more rapid and prolonged increase, lasting for at least 7 days, was observed in EMR86 lymph node and lung metastases. In both models, no effect was observed after sham surgery (consisting of opening and closing of the skin under anesthesia). Removal of MCR86 tumors (growing in the hind leg muscle) also resulted in a rapid, transient LI increase in metastases. Continuous BrdUrd labeling experiments in this tumor model did not favor the hypothesis that the LI increase predominantly resulted from an increase in the growth fraction. Moreover, in this model, the effect was related to operation trauma. A similar increase in LI, although smaller than after tumor removal, was seen after major surgical trauma in MCR83 flank tumors. These results indicate that in the rat, tumor removal and/or major surgical trauma may modulate the cytokinetics of distant metastases significantly. A study of the systemic, possibly endocrine, factors involved in the growth-stimulating effect of surgical trauma in these rat tumor models may help to assess the clinical relevance of these findings for patients with breast cancer.