Can we use UART COMMUNICATION with MCP23017?
I can think of one way.
In theory you could use the GPIO pins of the mcp23017 to control a couple of 2-way multiplexers. With these multiplexers you could split your Rx/Tx pins to more than one serial bus.
May it be obvious that you cannot used the split busses at the same time. So depending on your specific use-case this may or may not be a solution.