A novel classification of lung cancer into molecular subtypes.

The remarkably heterogeneous nature of lung cancer has become more apparent over the last decade. In general, advanced lung cancer is an aggressive malignancy with a poor prognosis. The discovery of multiple molecular mechanisms underlying the development, progression, and prognosis of lung cancer, however, has created new opportunities for targeted therapy and improved outcome. In this paper, we define "molecular subtypes" of lung cancer based on specific actionable genetic aberrations. Each subtype is associated with molecular tests that define the subtype and drugs that may potentially treat it. We hope this paper will be a useful guide to clinicians and researchers alike by assisting in therapy decision making and acting as a platform for further study. In this new era of cancer treatment, the 'one-size-fits-all' paradigm is being forcibly pushed aside-allowing for more effective, personalized oncologic care to emerge.

Regulation of p53 function by lysine methylation.

The reversible and dynamic methylation of proteins on lysine residues can greatly increase the signaling potential of the modified factor. In addition to histones, several other nuclear factors such as the tumor suppressor and transcription factor p53 undergo lysine methylation, suggesting that this modification may be a common mechanism for modulating protein­protein interactions and key cellular signaling pathways. This article focuses on how lysine methylation events on the C-terminal tail of p53 are generated, sensed and transduced to modulate p53 functions.

Methylation of the retinoblastoma tumor suppressor by SMYD2.

The retinoblastoma tumor suppressor (RB) is a central cell cycle regulator and tumor suppressor. RB cellular functions are known to be regulated by a diversity of post-translational modifications such as phosphorylation and acetylation, raising the possibility that RB may also be methylated in cells. Here we demonstrate that RB can be methylated by SMYD2 at lysine 860, a highly conserved and novel site of modification. This methylation event occurs in vitro and in cells, and it is regulated during cell cycle progression, cellular differentiation, and in response to DNA damage. Furthermore, we show that RB monomethylation at lysine 860 provides a direct binding site for the methyl-binding domain of the transcriptional repressor L3MBTL1. These results support the idea that a code of post-translational modifications exists for RB and helps guide its functions in mammalian cells.

The MBT repeats of L3MBTL1 link SET8-mediated p53 methylation at lysine 382 to target gene repression.

The p53 tumor suppressor protein is regulated by multiple post-translational modifications, including lysine methylation. We previously found that monomethylation of p53 at lysine 382 (p53K382me1) by the protein lysine methyltransferase (PKMT) SET8/PR-Set7 represses p53 transactivation of target genes. However, the molecular mechanism linking p53K382 monomethylation to repression is not known. Here we show in biochemical and crystallographic studies the preferential recognition of p53K382me1 by the triple malignant brain tumor (MBT) repeats of the chromatin compaction factor L3MBTL1. We demonstrate that SET8-mediated methylation of p53 at Lys-382 promotes the interaction between L3MBTL1 and p53 in cells, and the chromatin occupancy of L3MBTL1 at p53 target promoters. In the absence of DNA damage, L3MBTL1 interacts with p53K382me1 and p53-target genes are repressed, whereas depletion of L3MBTL1 results in a p53-dependent increase in p21 and PUMA transcript levels. Activation of p53 by DNA damage is coupled to a decrease in p53K382me1 levels, abrogation of the L3MBTL1-p53 interaction, and disassociation of L3MBTL1 from p53-target promoters. Together, we identify L3MBTL1 as the second known methyl-p53 effector protein, and provide a molecular explanation for the mechanism by which p53K382me1 is transduced to regulate p53 activity.

Modulation of p53 function by SET8-mediated methylation at lysine 382.

Reversible covalent methylation of lysine residues on histone proteins constitutes a principal molecular mechanism that links chromatin states to diverse biological outcomes. Recently, lysine methylation has been observed on nonhistone proteins, suggesting broad cellular roles for the enzymes generating and removing methyl moieties. Here we report that the lysine methyltransferase enzyme SET8/PR-Set7 regulates the tumor suppressor protein p53. We find that SET8 specifically monomethylates p53 at lysine 382 (p53K382me1). This methylation event robustly suppresses p53-mediated transcription activation of highly responsive target genes but has little influence on weak targets. Further, depletion of SET8 augments the proapoptotic and checkpoint activation functions of p53, and accordingly, SET8 expression is downregulated upon DNA damage. Together, our study identifies SET8 as a p53-modifying enzyme, identifies p53K382me1 as a regulatory posttranslational modification of p53, and begins to dissect how methylation may contribute to a dynamic posttranslational code that modulates distinct p53 functions.

The bifunctional FtsK protein mediates chromosome partitioning and cell division in Caulobacter.

Bacterial chromosome partitioning and cell division are tightly connected cellular processes. We show here that the Caulobacter crescentus FtsK protein localizes to the division plane, where it mediates multiple functions involved in chromosome segregation and cytokinesis. The first 258 amino acids of the N terminus are necessary and sufficient for targeting the protein to the division plane. Furthermore, the FtsK N terminus is required to either assemble or maintain FtsZ rings at the division plane. The FtsK C terminus is essential in Caulobacter and is involved in maintaining accurate chromosome partitioning. In addition, the C-terminal region of FtsK is required for the localization of the topoisomerase IV ParC subunit to the replisome to facilitate chromosomal decatenation prior to cell division. These results suggest that the interdependence between chromosome partitioning and cell division in Caulobacter is mediated, in part, by the FtsK protein.

Rapid and sequential movement of individual chromosomal loci to specific subcellular locations during bacterial DNA replication.

The chromosomal origin and terminus of replication are precisely localized in bacterial cells. We examined the cellular position of 112 individual loci that are dispersed over the circular Caulobacter crescentus chromosome and found that in living cells each locus has a specific subcellular address and that these loci are arrayed in linear order along the long axis of the cell. Time-lapse microscopy of the location of the chromosomal origin and 10 selected loci in the origin-proximal half of the chromosome showed that during DNA replication, as the replisome sequentially copies each locus, the newly replicated DNA segments are moved in chronological order to their final subcellular destination in the nascent half of the predivisional cell. Thus, the remarkable organization of the chromosome is being established while DNA replication is still in progress. The fact that the movement of these 10 loci is, like that of the origin, directed and rapid, and occurs at a similar rate, suggests that the same molecular machinery serves to partition and place many, if not most, chromosomal loci at defined subcellular sites.

Use of the Caulobacter crescentus genome sequence to develop a method for systematic genetic mapping.

The functional analysis of sequenced genomes will be facilitated by the development of tools for the rapid mapping of mutations. We have developed a systematic approach to genetic mapping in Caulobacter crescentus that is based on bacteriophage-mediated transduction of strategically placed antibiotic resistance markers. The genomic DNA sequence was used to identify sites distributed evenly around the chromosome at which plasmids could be nondisruptively integrated. DNA fragments from these sites were amplified by PCR and cloned into a kanamycin-resistant (Kan(r)) suicide vector. Delivery of these plasmids into C. crescentus resulted in integration via homologous recombination. A set of 41 strains containing Kan(r) markers at 100-kb intervals was thereby generated. These strains serve as donors for generalized transduction using bacteriophage phiCr30, which can transduce at least 120 kb of DNA. Transductants are selected with kanamycin and screened for loss of the mutant phenotype to assess linkage between the marker and the site of the mutation. The dependence of cotransduction frequency on sequence distance was evaluated using several markers and mutant strains. With these data as a standard, previously unmapped mutations were readily localized to DNA sequence intervals equivalent to less than 1% of the genome. Candidate genes within the interval were then examined further by subcloning and complementation analysis. Mutations resulting in sensitivity to ampicillin, in nutritional auxotrophies, or temperature-sensitive growth were mapped. This approach to genetic mapping should be applicable to other bacteria with sequenced genomes for which generalized transducing phage are available.