To better characterize bortezomib-regulated phosphoproteins, we classified all the differentially expressed phosphoproteins (DEPPs) into 23 functional categories according to the PANTHER system. These proteins are implicated in a broad range of cellular activities (Fig. 3A ). Next to the unclassified proteins (17%), proteins involved in nucleic acid binding account for the second largest portion (14%). There are also a significant number of proteins involved in receptor (10%), regulatory molecule (6%), and kinase (5%). Previous studies indicated that bortezomib exerts its anticancer function by inhibiting protein degradation in cancer cells [22] . In this connection, many bortezomib-regulated phosphoproteins found in current study were nucleic acid binding (14%) and transcription factors (4%), as shown in Figure 3A . These data suggest that the cancer-inhibitory effect of bortezomib may also rely on its regulatory role in mRNA transcription. Table S2 only shows a list of all borterzomib regulated phosphoproteins in MM cells. It lacks the biochemical context. To create significance out of otherwise static proteomic data, we constructed an interaction networking of the DEPPs (Fig. 3B) . The DEPPs were linked by various evidences based on neighborhood analysis, experimental results or text-mining. These relationships are color coded, and the legends are provided next to the map. This does not mean that all the interactions took place within a single spatial and temporal situation, but it enables the identification of central nodes in these DEPPs. Notably, stathmin was a hub in this network, suggesting that stathmin may play an important role in mediating bortezomib-induced apoptosis in MM cells. Some proteins remained orphans because there is insufficient information in the database to link them to other proteins in the network.