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Petr Kalab, Ph.D.

Portait Photo of Petr Kalab
Laboratory of Cellular and Molecular Biology
Center for Cancer Research
National Cancer Institute
Building 37, Room 2050
Bethesda, MD 20892-4256


Dr. Petr Kalab received C.Sc. (Ph.D. equivalent) from the Institute of Animal Physiology and Genetics of the Czech Academy of Sciences in 1990. During his postdoctoral visit at the University of Pennsylvania, Philadelphia, and in his own lab in Czech Republic, he studied signal transduction in mammalian reproduction. In 1997, Dr. Kalab redirected his career and as a visiting fellow at NICHD, NIH, Bethesda, and later as staff researcher at the University of California, Berkeley, focused on the mitotic functions of the small GTPase Ran. In 2008, Dr. Kalab joined the Laboratory of Cellular and Molecular Biology, NCI, NIH as a tenure-track investigator.


My research focuses on two organelles that are characteristic of the internal structure of eukaryotic cells: the nucleus and the mitotic spindle. In particular, it is fascinating that the essential roles of both these organelles require the contribution of a single signaling network controlled by the small GTPase Ran. Because of its fundamental influence, the analysis of Ran-regulated functions provides unparalleled opportunities to study the assembly and function of interphase nuclei and mitotic spindles.

In addition to its interphase role as the key regulator of transport between nucleus and cytoplasm, Ran also has many important functions during the mitotic phase of the cell cycle, including mitotic spindle assembly and re-formation of the nuclear envelope at the exit from mitosis. Many of the cellular functions of Ran depend on the intracellular organization of the GTP/GDP cycle on Ran. RCC1, the guanine nucleotide exchange factor for Ran, is a nuclear protein that binds to chromatin in mitotic cells, while RanGAP1 and its co-factors RanBP1 and RanBP2 are cytoplasmic. As a result, chromosomes are surrounded by the highest cellular concentration of RanGTP throughout the cell cycle. In interphase, the step-wise RanGTP gradients across the nuclear envelope provide direction to Ran-regulated nuclear transport. In mitosis, the diffusion-limited chromosomal RanGTP gradients promote mitotic spindle assembly and its correct localization within cells. The functions of the RanGTP gradient are mediated by the interaction of RanGTP with members of the family of nuclear transport receptors (NTRs) of the importin beta superfamily.

Growing evidence indicates that Ran and several NTRs are overexpressed in a variety of human cancers, contributing to tumor progression and metastasis. In addition, Ran is involved in the mitotic roles of proteins with diverse involvements in cancer cell biology, such as BRCA1, HURP, NUSAP, TPX2 and its downstream target Aurora A.

Recently, we used fluorescence lifetime imaging microscopy (FLIM) with FRET biosensors for RanGTP to measure the differences in mitotic Ran signaling in a variety of human somatic cells. We found that steep RanGTP gradients around mitotic chromosomes were detectable only in rapidly proliferating types of cells, whether they were normal or transformed. In contrast, the mitotic RanGTP gradients were not detectable or were significantly reduced in slow growing cells (Hasegawa et al., J. Cell Biol. 2013, 200(2):151-61). We showed that the increased expression of RCC1 and a large increase of chromosome number (both characteristic to cancer cells) were sufficient to drive the rise of steep mitotic RanGTP gradients. Because the RCC1-driven high RanGTP levels persist throughout the cell cycle, RanGTP could accelerate cell cycle via its essential role in the nuclear transport of cell cycle rate-limiting factors. Whether through the interphase or mitotic functions of Ran, increased RanGTP levels could therefore promote the proliferative hallmark of cancer cells.

Postdoctoral position is available

Postdoctoral position is available to investigate the cancer cell-specific mechanisms of mitosis regulation by Ran GTPase . We are looking for someone who will take over a project that is already well advanced and could be completed within several months. This research will involve the application of advanced live cell imaging methods (FLIM, FCS, FRAP, 4D spinning disc confocal) in normal and cancer cells, quantitative analysis of the data and variety of cell biological methods. The data from live cell imaging will be applied in a computational model of mitotic Ran system in aneuploid cancer cells that we are developing in collaboration with Dr. David Odde (University of Minnesota;

This position is available immediately, and the appointment will be for one year. Preferred starting date is before July 31, 2014.

* A) Applicants should be less than 4 years past Ph.D. in physics, biophysics of cellular and molecular biology.
* B) Proven expertise in live cell imaging and its quantitative analysis is essential. Proficiency in computational modeling would be an advantage.
* C) Good written and oral communication skills

Interested applicants should send CV with bibliography and contacts for 3 references to

This page was last updated on 6/17/2014.