The proliferation marker pKi-67 becomes masked to MIB-1 staining after expression of its tandem repeats

[Ki-67 -- new faces of an old player]

The Ki-67 protein was isolated twenty-five years ago and has become the first histological marker of proliferating cells until now. This molecule with a unique structure possesses such fundamental biological functions that are essential for normal cell proliferation. Since the Ki-67 protein is present in every dividing cell (G1, S, G2/M phase) but is absent from the resting cells (G0 phase) it is very much suitable for identifying the proliferating fraction of cells. Thus, it provides essential information concerning the malignancy of a tumor and about the prediction of response to a certain therapy. Based on its important role in cell proliferation, the Ki-67 protein might also play a role in tumor genesis. In their present work the authors discuss the history and the properties of Ki-67, its role in cell cycle regulation and its prognostic importance in different malignant disorders.

Membranous and cytoplasmic staining of Ki67 is associated with HER2 and ER status in invasive breast carcinoma

AIMS

Membranous and cytoplasmic Ki67 immunoreactivity has recently been observed in a number of histopathological entities, but frequency of occurrence and relationship to prognosis in more common cancers have not been described. The aim was to describe the pattern and frequency of membranous/cytoplasmic Ki67 in a cohort of invasive breast carcinomas, and their associations with grade, HER2 amplification and oestrogen receptor (ER) expression.

METHODS AND RESULTS

Three hundred and twenty-two cases of invasive ductal carcinoma were assessed for histological grade, Ki67 (MIB-1 clone) proliferation index and pattern of immunoreactivity, ER expression by immunohistochemistry, and HER2 amplification status by fluorescence in situ hybridization. Overall, 26/322 (8%) breast carcinomas showed membranous/cytoplasmic Ki67, and expression was significantly associated with grade 3, HER2-amplified and ER- tumours. Membranous/cytoplasmic Ki67 was not, however, an independent prognostic factor on multivariate analysis.

CONCLUSIONS

Membranous/cytoplasmic Ki67 identifies a group of breast carcinomas that may be important to consider separately in prognostic and predictive studies. The mechanism of subcellular Ki67 relocalization remains elusive and further studies are required to establish both the cause and effect of this unusual pattern of Ki67 immunoreactivity.

Proliferation marker pKi-67 occurs in different isoforms with various cellular effects

The Ki-67 antigen, pKi-67, is a commonly used proliferation marker in research and pathology. It has been recognized that the protein exists in two different splice variants that differ in one exon. In the current work, we present three new splice variants of human pKi-67 consisting of two naturally occurring isoforms and one atypical version. Additionally, data is presented indicating that alternative splicing of the pKi-67 N-terminus is common in tumor cell lines. Analyzing 93 tissues mainly consisting of brain tumor specimens, we found evidence that long and short isoform can be expressed independently of each other. Induction of mitosis in human peripheral blood mononuclear cells revealed that short pKi-67 appears earlier in the cell cycle than the long isoform and reaches its expression maximum when transcription of the latter sets in. Finally, transfection of mammalian culture cells with exon 7 (specific for the long pKi-67 isoform and not present in the short isoform) in a tetracycline regulated expression system decreased the rate of cell proliferation without affecting the cell cycle. In summary, we present evidence that the pKi-67 N-terminus is differentially spliced resulting in at least five different isoforms with different functions.

High-level mRNA quantification of proliferation marker pKi-67 is correlated with favorable prognosis in colorectal carcinoma

PURPOSE

The present study retrospectively examines the expression of pKi-67 mRNA and protein in colorectal carcinoma and their correlation to the outcome of patients.

METHODS

Immunohistochemistry and quantitative RT-PCR were used to analyze the expression of pKi-67 in 43 archival specimens of patients with curatively resected primary colorectal carcinoma, who were not treated with neo-adjuvant therapy.

RESULTS

We determined a median pKi-67 (MIB-1) labeling index of 31.3% (range 10.3-66.4%), and a mean mRNA level of 0.1769 (DeltaC(T): range 0.01-0.69); indices and levels did not correlate. High pKi-67 mRNA DeltaC(T) values were associated with a significantly favorable prognosis, while pKi-67 labeling indices were not correlated to prognostic outcome. A multivariate analysis of clinical and biological factors indicated that tumor stage (UICC) and pKi-67 mRNA expression level were independent prognostic factors.

CONCLUSION

Quantitatively determined pKi-67 mRNA can be a good and new prognostic indicator for primary resected colorectal carcinoma.

Innovative techniques and applications in histochemistry and cell biology

Recent studies documenting novel histochemical methods and applications in cell biology and in other areas of the life sciences have again rendered insights into structure and functions of tissues, cells, and cellular components to the level of proteins and genes. Particularly, sophisticated microscopic techniques have proved to be able to significantly advance our knowledge. Findings of recent investigations representing this progress are summarized in the present review.

Colorectal carcinomas with high MIB-1 labelling indices but low pKi67 mRNA levels correlate with better prognostic outcome

AIMS

Antibodies specific to the proliferation-associated protein pKi67 (e.g. Ki67, MIB-1) are routinely used in oncology to assess the proliferation index of tumour cells. In untransformed cells the amount of pKi67 present at any time of the cell cycle is strictly regulated. To achieve a better understanding of expression and regulation of this protein in tumour cells, we investigated both pKi67 mRNA and protein expression in routinely fixed and embedded tissue of colorectal carcinoma.

METHODS AND RESULTS

We determined a median pKi67 specific in-situ hybridization labelling index of 42% (9-79%) and a median Ki67 index (MIB-1 labelling index) of 59% (26-94%) in 47 resected colorectal adenocarcinomas of different stages and grades. In 32 cases expression of pKi67 mRNA and protein correlated well but we observed a significant difference between both values in 15 tumours. In these cases more than 30% of the cells expressed the protein but not the mRNA of pKi67, possibly due to cell cycle arrest. Patients belonging to this group had a significantly (P < 0.012) better prognosis.

CONCLUSIONS

Tumours with a high pKi67 protein level but low mRNA expression are likely to proliferate more slowly than calculated on the basis of their Ki67 staining index, which possibly explains the patients' improved outcome.

Progress in focus: recent advances in histochemistry and cell biology

Advances in histochemical and cell biological techniques enable increasingly refined investigations into the cellular and subcellular distribution of specific molecules and into their role in dynamic processes; thus progress in these fields complements the growing knowledge in genomics and proteomics. The present review summarizes recent technical progress and novel applications.